Top rebase Questions

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2521
Laurie Young

I stupidly did a Git commit while half asleep, and wrote the totally wrong thing in the commit message. How do I change the commit message?

I have not yet pushed the commit to anyone.

Answered By: bueno ( 2708)
git commit --amend -m "New commit message"

Used to amend the tip of the current branch. Prepare the tree object you would want to replace the latest commit as usual (this includes the usual -i/-o and explicit paths), and the commit log editor is seeded with the commit message from the tip of the current branch. The commit you create replaces the current tip -- if it was a merge, it will have the parents of the current tip as parents -- so the current top commit is discarded.

It is a rough equivalent for:

$ git reset --soft HEAD^
$ ... do something else to come up with the right tree ...
$ git commit -c ORIG_HEAD

but can be used to amend a merge commit.

366
webmat

Does anybody know how to easily undo a git rebase?

The only way that comes to mind is to go at it manually:

  • git checkout the commit parent to both of the branches
  • then create a temp branch from there
  • cherry-pick all commits by hand
  • replace the branch in which I rebased by the manually-created branch

In my current situation this is gonna work because I can easily spot commits from both branches (one was my stuff, the other was my colleague's stuff).

However my approach strikes me as suboptimal and error-prone (let's say I had just rebased with 2 of my own branches).

Any ideas?

Clarification: I'm talking about a rebase during which a bunch of commits were replayed. Not only one.

Answered By: Charles Bailey ( 500)

The easiest way would be to find the head commit of the branch as it was immediately before the rebase started in the reflog...

git reflog

and to reset the current branch to it (with the usual caveats about being absolutely sure before reseting with the --hard option).

# Suppose the old commit was HEAD@{5} in the ref log
git reset --hard HEAD@{5}

You can check the history of the candidate old head by just doing a git log HEAD@{5} .

If you've enabled per branch reflogs you should be able to simply do git reflog branchname@{1} as a rebase detaches the branch head before reattaching to the final head. I would double check this, though as I haven't verified this recently. You can do this by adding:

[user]
    logallrefupdates=true

I've been using git now for a couple months on a project with one other developer. I have several years of experience with svn, so I guess I bring a lot of baggage to the relationship.

I have heard that git is excellent for branching and merging, and so far, I just don't see it. Sure, branching is dead simple, but when I try to merge, everything goes all to hell. Now, I'm used to that from svn, but it seems to me that I just traded one sub-par versioning system for another.

My partner tells me that my problems stem from my desire to merge willy-nilly, and that I should be using rebase instead of merge in many situations. For example, here's the workflow that he's laid down:

clone the remote repo
git checkout -b my_new_feature
..work and commit some stuff
git rebase master
..work and commit some stuff
git rebase master
..finish the feature
git checkout master
git merge my_new_feature

Essentially, create a feature branch, ALWAYS rebase from master to the branch, and merge from the branch back to master. Important to note is that the branch always stays local.

Here is the workflow that I started with

clone remote repo
create my_new_feature branch on remote repo
git checkout -b --track my_new_feature origin/my_new_feature
..work, commit, push to origin/my_new_feature
git merge master (to get some changes that my partner added)
..work, commit, push to origin/my_new_feature
git merge master
..finish my_new_feature, push to origin/my_new_feature
git checkout master
git merge my_new_feature
delete remote branch
delete local branch

There are 2 essential differences (I think): I use merge always instead of rebasing, and I push my feature branch (and my feature branch commits) to the remote repo.

My reasoning for the remote branch is that I want my worked backed up as I'm working. Our repo is automatically backed up and can be restored if something goes wrong. My laptop is not, or not as thoroughly. Therefore, I hate to have code on my laptop that's not mirrored somewhere else.

My reasoning for the merge instead of rebase is that merge seems to be standard and rebase seems to be an advanced feature. My gut feeling is that what I'm trying to do is not an advanced setup, so rebase should be unnecessary. I've even perused the new Pragmatic Programming book on git, and they cover merge extensively and barely mention rebase.

Anyways, I was following my workflow on a recent branch, and when I tried to merge it back to master, it all went to hell. There were tons of conflicts with things that should have not mattered. The conflicts just made no sense to me. It took me a day to sort everything out, and eventually culminated in a forced push to the remote master, since my local master has all conflicts resolved, but the remote one still wasn't happy.

What is the "correct" workflow for something like this? Git is supposed to make branching and merging super-easy, and I'm just not seeing it.

Update 2011-04-15

This seems to be a very popular question, so I thought I'd update with my 2 years experience since I first asked.

It turns out that the original workflow is correct, at least in our case. In other words, this is what we do and it works:

clone the remote repo
git checkout -b my_new_feature
..work and commit some stuff
git rebase master
..work and commit some stuff
git rebase master
..finish the feature
git checkout master
git merge my_new_feature

In fact, our workflow is a little different, as we tend to do squash merges instead of raw merges. This allows us to turn our entire feature branch into a single commit on master. Then we delete our feature branch. This allows us to logically structure our commits on master, even if they're a little messy on our branches. So, this is what we do:

clone the remote repo
git checkout -b my_new_feature
..work and commit some stuff
git rebase master
..work and commit some stuff
git rebase master
..finish the feature
git checkout master
git merge --squash my_new_feature
git branch -D my_new_feature

I've come to love git and never want to go back to SVN. If you're struggling, just stick with it and eventually you'll see the light at the end of the tunnel.

Answered By: VonC ( 143)

"Conflicts" mean "parallel evolutions of a same content". So if it goes "all to hell" during a merge, it means you have massive evolutions on the same set of files.

The reason why a rebase is then better than a merge is that:

  • you rewrite your local commit history with the one of the master (and then reapply your work, resolving any conflict then)
  • the final merge will certainly be a "fast forward" one, because it will have all the commit history of the master, plus only your changes to reapply.

I confirm that the correct workflow in that case (evolutions on common set of files) is rebase first, then merge.

However, that means that, if you push your local branch (for backup reason), that branch should not be pulled (or at least used) by anyone else (since the commit history will be rewritten by the successive rebase).


On that topic (rebase then merge workflow), barraponto mentions in the comments two interesting posts, both from randyfay.com:

Using this technique, your work always goes on top of the public branch like a patch that is up-to-date with current HEAD.

(a similar technique exists for bazaar)

When does one use git rebase vs git merge?

Does one still need to merge after a successful rebase?

Answered By: Rob Di Marco ( 152)

Short Version

  • Merge takes all the changes in one branch and merge them into another branch in one commit.
  • Rebase says I want the point at which I branched to move to a new starting point

So when do you use either one?

Merge

  • Let's say you have created a branch for the purpose of developing a single feature. When you want to bring those changes back to master, you probably want merge (you don't care about maintaining all of the interim commits).

Rebase

  • A second scenario would be if you started doing some development and then another developer made an unrelated change. You probably want to pull and then rebase to base your changes from the current version from the repo.