What does -u mean in Git?

Question

git

for example, what does -u mean in the git push -u origin master command?

Answer 1

git push --help ? no, I didn't hear it!!!!

-u, --set-upstream
For every branch that is up to date or successfully pushed, add upstream (tracking) reference, used by argument-less git-
pull(1) and other commands. For more information, see branch..merge in git-config(1).

What is the difference between git push -u origin master and git push origin master? Why the -u switch for the git push command?