How to use patch

Patch Single file:
   make a patch:
       cd program_folder        # go into the target folder
       diff -Nu old_file new_file > patch_file
       # the patch_file is the patch, it can use to patch file for another user
   patch a file:
       cd program_folder        # go into the target folder
       patch -p 1 < patch_file
       # if you want to UnPatch the file
       patch -R -p 1 < patch_file

Patch a Directory:
   make a patch:
       diff -rNu old_folder new_folder > patch_file
       # no need to exec the command inside the program folder
   patch the folder:
       patch -p 0 < patch_file
       # if you want to UnPatch, also use -R
       patch -R -p 0 <>