Yeah, the directive is having an effect ... the value of the variable is whatever I set it to be, and otherwise the variable doesn't exist ... but the name is changed.

Yes, you are absolutely correct that environment-variables can be set with $ENV{}, and that many desirable magickal effects happen when you do so within a BEGIN { } block, because of the (very early...) point in time when Perl considers such blocks. This is an apparently-valid, and therefore very-important, observation. Let us therefore recognize it, and let it stand.

But my particular question in this post is... where and why does “REDIRECT_” come from? Why is the final name of the environment-variable not the name that I have attempted to set?