As I discussed here, git allows you to commit only some of the changes you made to a given file. If you are working in Emacs you probably already know the wonders of Magit. In order to do the same partial committing of a file you can simply open magit-status and go to the file you’re interested in. This will highlight the changed parts of the text. With your cursor in the changed block you’d like to commit simply press s and that change will be staged. If this is all you want press c to commit and you’re done!