and
.I foo
might be directory hierarchies or single files.
If you are creating a patch file for
.B patch
to use, you should put the old file/directory first, and the
new file/directory second: for example
.B diff
-u old-file new-file
or
-ur old-directory new-directory
.SH SEE ALSO
cmp(1), comm(1), diff3(1), ed(1), patch(1), pr(1), sdiff(1).
.SH DIAGNOSTICS