The Ten Minute Guide to diff and patch Situation one: you are trying to compile a package from source and you discover that somebody has already done the work for you of modifying it slightly to compile on your system. They have made their work available as a "patch", but you're not sure how to make use of it. The answer is that you apply the patch to the original source code with a command line tool called, appropriately, patch. Situation two: you have downloaded the source code to an open source package and after an hour or so of minor edits, you manage to make it compile on your system. You would like to make your work available to other programmers, or to the authors of the package, without redistributing the entire modified package. Now you are in a situation where you need to create a patch of your own, and the tool you need is diff. This is a quick guide to diff and patch which will help you in these situations by describing the tools as they are most commonly used. It tells you enough to get started right away. Later, you can learn the ins and outs of diff and patch at your leisure, using the man pages. Applying patches with patch To apply a patch to a single file, change to the directory where the file is located and call patch: atch &lt; foo.patch These instructions assume the patch is distributed in unified format, which