Looks like -u can take an extra number argument, but I don't quiet get the manual, It says,  -u, -U NUM, --unified[=NUM]          output NUM (default 3) lines of unified contextSomeone name an example please? I couldn't find a working one.
What does -u of diff really do?
diff
-u by itself outputs results in unified format the number just changes the number of neighboring lines included as context.