Somewhat OT...

My documentation assumes my users don't know there is a slash/backslash issue, and tells them explicitly to use slashes. Otherwise many (most?) of them would use backslashes, but only single backslashes, and then complain the script is broken.

Getting strings back from other code, or feeding strings to other code (e.g., system) should be checked. If you do this a lot, you might create some data structure that you can use to filter requests and returns. When something changes, you change your File::Backslash module. (Or better, have it do the right thing based on versions.)