Creating a Patch File:
diff -Naur oldfile newfile >patch_file

Patching a File:
patch -p0

Note about patch levels (-p0, -p1, -p2, -p3, ..)

The -p option will optionally strip off directory levels from the patchfile. For Ex: if you have a patchfile with a header as such:

Using a -p0 will expect, from your current working directory, to find a subdirectory called “new”, then “modules” below that, then the “pcitable” file below that.

Using a -p1 will strip off the 1st level from the path and will expect to find (from your current working directory) a directory called “modules”, then a file called “pcitable”. Patch will ignore the “new” directory mentioned in the header of the patchfile.

Using a -p2 will strip of the first two levels from the path. Patch will expect to find “file” in the current working directory. Patch will ignore the “new” and “modules” directories mentioned in the header of the patchfile.

Using a -p3 in this example would not be a good thing. Patch probably wouldn’t patch anything.