[rant]
All this highlights one of my long-standing (personal) "aestetical" issues with those two files: Starting with the principle that settings that have similar function should have also similarly named setting files and furthermore similar content, I personally would prefer if '/opt/.backup_device' (with a content like 'hda1/tce') would rather be '/opt/.backup_file' (with a content like '/mnt/hda1/tce/mydata.tgz').
This way (at least IMHO) the information does not require further processing to be actually useful (e.g.
ls -l $(cat /opt/.backup_file)). I accept that nothing is "seriously broken" in the current state, but it requires (again IMHO) more "brain gymnastics" to follow the relevant scripts.
And whilst I'm already on a roll: Why do those files have to be hidden? And what's the point of them being in '/opt' which is IMHO an "obvious violation" of the
Filesystem Hierarchy Standard[/rant]