How to make branch B exactly like branch A?

Question

Say I have an existing branch B (if it makes a difference, it's remote).

I also have a branch A (either local or remote). I would like branch B to be exactly like A. If I understand correctly, merge doesn't make the branches identical, there still can be something in branch B that wasn't on branch A and it will remain there after doing git checkout B followed by git merge A. Do I understand correctly?

Of course, I can just delete branch B and create a new branch B from A. Is that the best way?

note just to clarify it: I want to keep branch B alive because of deployment configuration. If I delete and recreate I'll need to do another thing manually for deployment.

Answer 1

git keeps track of the history of development. Thus, to make a branch exactly like another branch, you just need to:

git checkout <branch B>
git reset --hard <branch A>
git push --force origin <branch B>

Of course, doing this you will lose the development history that was on branch B.

Answer 2

Sounds like you just want to rename branchB.

git branch -m branchB new_name_for_branchB
git branch branchA branchB

Now new_name_for_branchB refers to the same commit that branchB used to, and branchB now refers to the same commit as branchA. The two branches A and B are still distinct, though.