Git - changing the branch tip to include commits from another branch

Question

I have a git workflow scenario question and have provided the "current" and "desired" branch structures, but I don't know the correct commands to get to the desired state.

Current:

a -- b                --> Branch1 (there are no commits after b)
     \
      \
       c -- d -- e    --> Branch2

I want to rebase or reset head (not merge, as I want a straight line history in log) such that Branch 1 looks like this:

Desired:

a -- b -- c -- d -- e --> Branch1
     \
      \
       c -- d -- e    --> Branch2 (this branch may be removed)

I realise that the head of Branch2 must now be the head of Branch1, but don't know if the following commands will ensure changes c and d will also become part of Branch1 or if the new commit history will look like a -- b -- e:

git checkout Branch1 
git reset Branch2

Thank you for your time!

You just need to move the pointer... the simples way to do it is git branch -F branch1 branch2 so that branch1 moves to the same commit that branch2 is pointing to. If you want to remove branch2 you might instead delete branch1 and renam branch2 to branch1: got branch -m branch2 branch1. It's the same end result as moving the pointer and then deleting branch2. — eftshift0
– eftshift0, Commented May 2, 2023 at 10:03
As a side note, I think you should say tip instead of head or HEAD. HEAD has a very special meaning in git: it's whatever commit/branch you are working on, and it's not necessarily pointing to a branch. — eftshift0
– eftshift0, Commented May 2, 2023 at 10:04
Thank you so much. For the benefit of anyone else who may come and read this, I found another link here that clarifies the difference between tip and HEAD in git: stackoverflow.com/questions/39752604/…. — Vada Poché
– Vada Poché, Commented May 2, 2023 at 10:14

YSC · Accepted Answer · 2023-05-02 10:05:55Z

3

Since Branch1 has no commits after b, you can simply fast-forward it to Branch2:

git checkout Branch1
git merge --ff-only Branch2

--ff-only forces a fast-forward and forbids a merge commit. See man git-merge#ff.

After the fast-forward, your tree will look like this:

a -- b -- c -- d -- e --> Branch1, Branch2

Branch2 can safely be removed. This whole operation is strictly equivalent to removing Branch1 and renaming Branch2 to Branch1. Remember, for git a branch is simply an alias/pointer to a commit.

answered May 2, 2023 at 10:05

YSC

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Comments

matt · Accepted Answer · 2023-05-02 10:37:30Z

3

Branches are just string names attached to some commit, and you can manipulate what commit a branch name is attached to.

So your formulation is basically right. Say this:

git switch Branch1 
git reset --hard Branch2
git branch -D Branch2

Alternatively you could use the first branch name to replace the second branch name:

git switch Branch2
git branch -M Branch1

edited May 2, 2023 at 10:37

answered May 2, 2023 at 10:28

matt

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4 Comments

Vada Poché Over a year ago

Thank you. Will this method also ensure that commits c and d are present in Branch1?

matt Over a year ago

Commits are not "present in a branch". The branch is just a name for one commit. Nothing but names are affected here.

Vada Poché Over a year ago

Thank you, much appreciated. I am slowly moving away from the 'SVN' way of thinking, so your comment is very helpful.

matt Over a year ago

Read my biteinteractive.com/… to discover what Git is and how to think about it

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