Frequently used in a command line interface, the diff command has been used for nearly 40 years as a file comparison tool. In this study, we test the effectiveness of the diff command line tool as a way to preview changes to different actions, or as a patch. We specifically look at the effectiveness in regards to selective undo: a manner of undoing previous actions in a non-linear way. Results found that users who were simply shown what the outcome of their patch would be were able to navigate the selective undo visualizations faster than than those who were shown diff statements.