I would re-consider this idea of not making a temporary file for the input. This simplifies the situation a lot. And prevents deadlocks that can occur in a single process while simultaneously feeding stuff in and reading stuff out.

The File::Temp module is multi-platform and generates a unique file name that you can use. The best is to delete this file yourself when you are finished with it, although this file will be created in a directory that is periodically cleaned-up - don't assume that file will be there for any significant length of time! - if you are a single user on Windows, you have to run the "file cleanup" utility yourself!

I would at least try making intermediate interface file before having to attempt complicated code to deal with this. You may be over-estimating the logistical requirements of a temporary interface file and under estimating the complexity of other solutions. The simple idea will be more easily portable.