Rolf, are you saying that the OP’s strategy would work?   I presume that you are referring to the paragraph in perldoc -f open which begins “Here is a script that saves, redirects, and restores "STDOUT" and "STDERR" using various methods:” but I do get pretty-lost pretty-fast when reading it.   Could you perhaps offer a couple of specific examples that do, specifically, what the OP has in mind to do?   Or, otherwise, elaborate on how you’d do it?