Creating a diff of two files and patching

In what case should you know what a diff is? Or a patch? In the Linux world, it is a way to determine the differences between files and also to solve problems at the OS level (especially if you have a broken driver in the Linux kernel). However, for the purposes of a cookbook, diffs and patches useful for a couple of main things:

• When determining whether a particular script or configuration file has modifications
• When plotting differences between versions, or migrating data between an old to new script, and so on

So, what is a diff or differential? A diff is the output that describes the differences between two files (file A and file B). The file A is the source, and the B file is the assumed to be modified file. If no diff output is created, then A and B are either empty or there are no differences. Diffs in a unified format typically...