Patching

Patching is a useful tool when sharing and dealing with source code changes, particularly in situations where there is a main or "trunk" code that multiple people are developing. A patch consists of a file that contains differences between two files or directories. In the case of multiple people modifying the same code base, people can share patches, which allows them to share fixes, modifications, or other changes, bundled together in a single file, rather than having to share every single file that's changed.

Life without patches

Imagine you have a 70,000-line file, and you only changed one line - why share 70,000 lines of code, instead of the 1 line you changed? It gets even worse if the person you're sharing your changes with has changed other lines in that file. Now he or she has to open up the two files, compare them side-by-side, and apply your changes to their code. It's a big hassle, and has a very high potential for someone to unintentionally blow away all their hard work.

Life with patches

You share a small patch file, which will apply the change to the 1 line you modified. The person you share it with need only apply the patch, and only that 1 line is touched.