Apply the output of the diff command to an original file.
patch [options] < patch_file
-c causes the patch file to be interpreted as a context diff.
-e forces patch to interpret the patch file as an ed script.
-f forces patch to be applied regardless of any inconsistencies.
-n causes the patch file to be interpreted as a normal diff.
-pn strips everything up to n slashes in the pathname.
-R indicates that patch file has been created with new and old files swapped.
-u causes the patch file to be interpreted as a unified diff.
-v displays the version number.
The patch command is used to update an original file by applying all the differences between the original and a revised version. The differences are in the form of an output from the diff command, stored in the patch_file. Changes to Linux kernel source code are distributed in the form of a patch file. Chapter 21 discusses how to apply patches to the kernel source.