I am backing up files, and I have a lot of files duplicated in multiple locations. I've used fdupes to find duplicates, but I'm actually looking for some sort of inverse of this tool.
I want to see if dir A and its sub directories contain any file that dir B does not contain. I'd like to see a list of files, if that would be possible, based on the contents of the file (comparing file size and hash).
Does any such tool already exist? (Or am I even approaching this completely wrong)