> Usability of diffs, to do actual useful tasks, is an excellent research topic. But a very difficult area. I use the linux command line `diff` to implement a

> Usability of diffs, to do actual useful tasks, is an excellent research topic. But a very difficult area. I use the linux command line `diff` to implement a poor mans database. An online file store has files added daily that I need to download but not duplicate, so I grab the list off the site, save it locally, and `diff local_downloaded_files current_list_on_site | grep '>' | tr -d'>'`.. The '>' symbol is an indication of files I haven't downloaded yet; the greater than is the operation I need to perform to make my local_downloaded_files file the same as the list on the site. So I download all the files that are indicated by the diff, add their names to local_downloaded_files file and voila, up to date downloads.