How do I rebase a chain of local git branches?

Question

Suppose I have a chain of local git branches, like this:

       master    branch1   branch2           |         |         | o----o----o----A----B----C----D 

I pull in an upstream change onto the master branch:

              branch1   branch2                  |         |             A----B----C----D            / o----o----o----o                |             master 

Now I rebase branch1, giving me this:

                        branch2                            |             A----B----C----D            /           o----o----o----o----A'---B'                |         |             master    branch1 

Note that because of rebasing branch1, commits A and B have been rewritten as A' and B'.

Here's my problem: now I want to rebase branch2. The obvious syntax is git rebase branch1 branch2, but that definitely does not work. What I want it to do is just reapply C and D on top of branch1, but instead it tries to reconcile A and A' and it considers them conflicting.

This does work:

git rebase --onto branch1 branch2^^ branch2 

This assumes I know that branch2 has exactly 2 commits beyond the previous branch1 ref.

Since git rebase --onto works, is there a 1-line git command that will rebase branch2 on top of a newly-rebased branch1, in a way that I don't have to know exactly how many commits were part of branch2? (I want to specify some magic ref instead of branch2^^ for the middle argument.)

Or is there some other approach I'm overlooking?

I would be most interested in a solution that scales well to extreme cases, not just two branches - suppose I've got something more like 5 local branches, all chained on one another, and I want to rebase all of them together.

Answer 1

One-line:

git rebase --onto branch1 branch1tmp branch2 

That supposes to make a branch1tmp on branch1 before rebasing branch1.

git checkout branch1 git branch branch1tmp git rebase master git rebase --onto branch1 branch1tmp branch2 

---

That being said, check what ORIG_HEAD references.
From git rebase man page:

ORIG_HEAD is set to point at the tip of the branch before the reset.

So check if this would work (and scale better):

git checkout branch1 git rebase master git rebase --onto branch1 ORIG_HEAD branch2 git rebase --onto branch2 ORIG_HEAD branch3 ...