Sometimes when comparing two directories, a file may exist in one
directory but not the other. If you give diff the
--new-file (-N) option, or if you supply an old or
new file that is named /dev/null or is empty and is dated the
Epoch (1970-01-01 00:00:00 UTC), diff outputs a patch that
adds or deletes the contents of this file. When given such a patch,
patch normally creates a new file or removes the old file.
However, when conforming to POSIX (see patch and the POSIX Standard),
patch does not remove the old file, but leaves it empty.
The --remove-empty-files (-E) option causes
patch to remove output files that are empty after applying a
patch, even if the patch does not appear to be one that removed the
file.
If the patch appears to create a file that already exists,
patch asks for confirmation before applying the patch.