Today, we’re diving into Git rebase, a tool that, once mastered, can help us manage branches in a clean and efficient manner, ensuring our commit history remains tidy and linear. We’ll discuss how to use Git rebase effectively, including practical tips and common pitfalls.

What is Git Rebase?

Git rebase is a way to move or combine a sequence of commits onto a new base commit. Picture it as the process of rearranging building blocks, where each block is a commit. Rebasing makes it look as if you started building from a new, updated foundation, while internally, Git is creating new commits and applying them to that new base.

Using Git rebase is particularly helpful when we need to make sure our work integrates well with recent changes from the main branch or when we want our history to appear linear, making it easier to follow. It’s essential to understand, though, that rebasing is a history-rewriting operation, which means we need to use it carefully to avoid potentially disastrous scenarios.

Why Use Git Rebase?

The primary motivation behind rebasing is to maintain a cleaner project history. Imagine we’re working on a feature branch, and while we’re hard at work, the main branch continues to evolve. We might have pulled the latest changes using Git merge, but each merge introduces a new commit that adds unnecessary clutter to the history. Git rebase, however, lets us rewrite our commits on top of the new main branch, making it look like we had been working off those latest changes all along.

In practical scenarios, this linear history helps us locate bugs and makes debugging less of a hassle. When we run commands like git log or git bisect, it’s much simpler to reason about a history that’s clean and free of extra merge commits. This neatness pays off when trying to track down when a bug was introduced—especially on larger projects.

How Git Rebase Works

To understand rebasing more clearly, let’s break down its basic usage with an example:

Suppose we have the following branch structure:

In this example, the main branch has four commits (A, B, C, and D), while our feature branch diverged from commit B and contains three new commits (E, F, and G).

When the main branch moves ahead to commit D, we may want our feature branch to start from there, effectively making it look like we’ve developed these features after all of main’s recent changes.

We do that with Git rebase:

After running the rebase command, our feature branch will look like this:

Git has replayed our commits (E, F, G) on top of the main branch, creating entirely new versions of those commits (notated as E’, F’, G’). This is a powerful way to make our history appear as if it always followed the latest version of the main branch.

Git essentially moves your feature branch to the tip of the main branch, reapplying each of your commits one by one, allowing you to incorporate all changes from the main branch without the need for an additional merge commit.

Git Rebase vs. Git Merge

Rebase and merge serve similar purposes—they help incorporate changes from one branch into another. But there are key differences:

Git Merge: When we merge branches, we create a new commit that represents the combination of changes, preserving the history of both branches. This makes for a non-linear history that can quickly become cumbersome to read if we frequently merge.

2. Git Rebase: Rebasing, on the other hand, creates a linear history. This gives the appearance that we built our features directly on the latest work in the main branch. The downside is that since it rewrites history, it’s unsuitable for changes that are already public, as this can lead to lost commits and confusion for collaborators.

Generally, we prefer merging for public branches, like the main branch, and rebasing for feature branches. This approach allows us to cleanly rebase and then merge with minimal clutter when we’re ready to integrate our work.

Interactive Rebase: Taking Full Control

One of the most powerful aspects of Git rebase is its interactive mode. With interactive rebasing, we can rewrite, edit, reorder, or squash commits, offering full control over what our history will look like.

To initiate an interactive rebase, we use:

git rebase -i HEAD~n

Here, HEAD~n refers to the last n commits we want to include in the rebase. Running this command will open an editor where we see a list of commits with various options for manipulation:

• pick: Use the commit as-is.
• reword: Edit the commit message.
• edit: Pause the rebase to change the commit itself.
• squash: Combine this commit with the one before it, keeping both changes.
• fixup: Similar to squash, but discard the current commit’s message.
• drop: Delete the commit.

Squashing Commits

Squashing commits is a common use case for interactive rebase. Suppose we made several tiny commits while working on a feature. We might want to consolidate them into a single commit before merging.

To squash commits, we choose the squash command for each commit we want to combine:

We can then edit the rebase file so that our commits are combined into one. After saving, Git will create a single, unified commit that represents all those changes, making our history cleaner and easier to read.

Reordering Commits

Interactive rebase also allows us to reorder commits. For instance, if the sequence of our changes doesn’t make logical sense, we can easily change the order in which commits are applied during an interactive rebase. This is particularly useful if we realized late that some features should logically be grouped together.

Best Practices and Avoiding Common Pitfalls

Never Rebase Public Branches

One of the golden rules of Git is that we should never rebase commits that have already been pushed to a shared repository. Rebasing rewrites commit history, and if someone else has based their work on the old history, they’ll have trouble when they pull changes—potentially resulting in lost work or tricky conflicts. When working with collaborators, rebasing should be restricted to local feature branches.

Using Restore Points

Git rebase can be daunting because changes are destructive, but we can always create a “restore point” before starting. One way to do this is to create a tag:

git tag <tagname>

In case something goes wrong, we can use 

git reset –hard <tagname> 

to restore the state before the rebase.

Managing Merge Conflicts During a Rebase

Merge conflicts are an inevitable part of rebasing, especially when multiple people are working on the same codebase. If a conflict arises during a rebase, Git will pause and let us resolve the conflict manually. Once we resolve the conflict, we use:

git rebase –continue

If things get too messy and we want to give up on the rebase, we can use:

git rebase –abort

This command will bring us back to the original state before starting the rebase, letting us start fresh.

Recovering from a Botched Rebase

Rebasing can go wrong, and it’s important to know how to recover. Fortunately, Git provides us with tools like git reflog, which tracks everything happening in our repository, even commits that appear lost.

If a rebase goes sideways, we can use git reflog to identify the previous state and then reset to that point:

git reflog show HEAD

This will output the HEAD reflog. You should see output similar to:

37656e1 HEAD@{0}: rebase -i (finish): returning to refs/heads/git_reflog

37656e1 HEAD@{1}: rebase -i (start): checkout origin/main

37656e1 HEAD@{2}: commit: some WIP changes

You can select your commit from this reflog and reset on it

git reset HEAD@{2}

This command will return our branch to the state it was in before the rebase, effectively undoing the operation.

Configuration Options for Git Rebase

There are a few configuration options we can set to make our rebasing process smoother:

• rebase.stat: This boolean flag controls whether a diffstat is shown during rebase. Setting this to true can be useful for visualizing the changes being applied.
• rebase.autoSquash: This option helps to automatically reorder and squash commits during an interactive rebase if we used –fixup in the commit message. This can be a great time-saver for tidying up commits.
• rebase.instructionFormat: This can be used to customize how commits are displayed during an interactive rebase, helping us understand the context of each change.

Conclusion

While git rebase can be daunting due to its destructive nature, understanding how it works, when to use it, and the risks involved makes it an invaluable part of our Git toolkit. Whether we’re integrating upstream changes, rewriting our commit history to make it more understandable, or squashing those unnecessary commits, Git rebase is there to help us keep things tidy.

Always use caution when rebasing shared branches, consider creating restore points, and remember that the goal is to make our history easy to understand for ourselves and for anyone else who might work on the project.

By mastering Git rebase, we gain more than just a way to manipulate commits, we gain the ability to make our project’s history a clear, navigable narrative of how our code came to be. Understanding the nuances of rebasing, knowing how to recover from issues, and utilizing interactive rebases gives us a powerful set of tools to ensure our Git workflows are clean, efficient, and reliable.