Git Rebase

What’s the difference between rebasing and merging? Well, let me tell you. Rebasing is changing the baseline for your changes, moving the point at which the branch started. This is an over-simplified view, but it’s far easier to mentally reconcile this than the official description of ‘forward porting’, and in my mind better describes how it’s likely to be used.

Moving the branch point with rebase allows you to integrate changes on other branches with yours while avoiding a merge and extraneous commits in the history. In a way, it fast-forwards your branch to silently incorporate movement on other branches.

If it’s that good, why wouldn’t you want do this all the time, and why is there a need for a merge command that does create history? It’s simple - sometimes you want a record of activity. Sometimes you want a workflow that prefers merges. And sometimes you don’t want to change history, which is basically what rebase is doing; if you’ve pushed your branch, rebase might be undesirable.

The documentation for rebase is located here: although it is rather dry as you might expect from a manual page.

Using rebase

git rebase

Aborting a failed rebase

If you have started a rebase and there are conflicts, you can either resolve them or abandon the rebase.

git rebase –abort

Completing a rebase after conflict resolution

When you need to finish off a rebase after making the alterations needed to satify a conflict, you’ll need to ask rebase to resume:

git rebase –continue

Interactive rebases

Interactively rebasing lets you choose what to do with each commit during the rebase if you know what you’re doing. Most commonly this is used to squash multiple commits into a single unit, and to write a useful message that covers the changes.

Squashing commits

Some tools like to have a changeset as a single commit. In particular this includes code review tools like Gerrit that have a strong preference towards this and actively encourage large changes in a single commit to facilitate reviews. The downside of squashing commits is the risk of losing messages and descriptions of the changes.

Conflict resolution

Sometimes (often?) when you rebase you’ll have conflicts. There are four ways to deal with this

  • Abandon the rebase with git rebase –abort

  • Manually resolve the conflict by editting the file and adding it with git add then resuming the rebase with git rebase –continue

  • Chose your file with git checkout –ours [filename]

  • Chose their file with git checkout –theirs [filename]

It should be noted that the meaning of ‘theirs’ and ‘ours’ depends on context; when rebasing, ‘ours’ often means the master branch, whereas ‘theirs’ means the branch with the changes, the one that is being rebased.