To apply an existing patch:
patch < patchfile
If you get an error, might need:
patch -p1 < patchfile
To apply an existing patch:
patch < patchfile
If you get an error, might need:
patch -p1 < patchfile
If you're into genealogy, it's sort of like a great-aunt twice removed -- the p is the removed.
Usually if you have trouble applying a patch, you can ask someone involved in the project what -p number they normally use.