Last checked against version &patch-contversion;. The patch program modifies a file according to a patch file. A patch file usually is a list, created by the diff program, that contains instructions on how an original file needs to be modified. Patch is used a lot for source code patches since it saves time and space. Imagine a package that is 1 MB in size. The next version of that package only has changes in two files of the first version. It can be shipped as an entirely new package of 1 MB or just as a patch file of 1 KB, which will update the first version to make it identical to the second version. So if the first version was downloaded already, a patch file avoids a second large download.