How Git Rebase Works?

Git is a powerful tool for version control, and one of its most valuable features for maintaining a clean and organized project history is git rebase. While merging is often the more straightforward choice, rebasing provides a way to streamline and tidy up your commit history, making it easier to review and collaborate on projects.

In this post, we’ll explore how git rebase works, when to use it, and go through the steps of a basic rebase, interactive rebase, and handling conflicts that may arise.

What is Git Rebase?

Rebasing is the process of moving or combining a sequence of commits to a new base commit. Instead of merging the branch history as-is, rebasing “rewrites” commit history by changing the starting point of a branch. This results in a more linear project history, where all commits appear sequentially, making it easier to understand the changes introduced over time.

Rebase vs. Merge: What’s the Difference?

• Merge: Combines branches while preserving the commit history from both. When you merge a feature branch into the main branch, Git adds a new “merge commit” to combine the histories.
• Rebase: Rewrites commit history to appear as if the branch was created directly from the latest commit on the target branch, resulting in a linear history without merge commits.

Pros of Using Rebase

• Cleaner History: Rebasing keeps the commit history cleaner and more readable, as there are no additional merge commits.
• Sequential Commits: With rebased commits, changes appear in a straight line, making it easier to understand the progression of changes.
• Easier Debugging: Linear history simplifies debugging and code review since there are fewer branches to follow.

When to Use Rebase

Rebasing is best used in the following scenarios:

1. Feature Branches: Rebasing feature branches onto the main branch helps keep a clean project history, especially when the feature branch is still in development.
2. Updating Feature Branches: If changes have been made to the main branch, rebasing onto it allows you to incorporate those changes without a merge commit.
3. Tidying Up Before Merging: Before merging a feature branch, rebasing it onto the main branch can simplify the history, ensuring the branch looks as if it was developed from the latest state of the main branch.

Note: It’s generally not recommended to rebase shared branches, as it can rewrite commit history, potentially causing issues for others working on the same branch.

How to Rebase a Branch

Let’s go through a basic rebase operation to better understand how it works.

Step 1: Check Out the Branch to Rebase

To begin, check out the branch you want to rebase. In this example, let’s assume you’re on a feature branch called feature-branch and want to rebase it onto main.

git checkout feature-branch

Step 2: Start the Rebase

Now, initiate the rebase onto the main branch:

git rebase main

Git will take the commits from feature-branch, starting from the point where it diverged from main, and replay them on top of the latest commit in main.

Step 3: Resolve Any Conflicts

If there are conflicts between the changes in feature-branch and main, Git will stop the rebase and ask you to resolve them. For each conflict, you can:

1. Edit the files to fix the conflicts.
2. Stage the resolved files using git add:

   git add <filename>

3. Continue the rebase:

   git rebase --continue

If you need to stop the rebase, you can cancel it with:

git rebase --abort

Step 4: Complete the Rebase

Once all conflicts are resolved, Git will apply the remaining commits, and the rebase will be complete. You now have a clean, linear history as if the feature branch was developed directly from the latest commit in main.

Interactive Rebase

Interactive rebase, a more advanced form of rebase, allows you to perform additional actions on commits, such as editing, reordering, squashing (combining), or even dropping commits. This can be especially useful for tidying up a feature branch before merging.

Step 1: Start an Interactive Rebase

To start an interactive rebase, use the -i flag followed by the commit you want to start rebasing from. Usually, this is the commit where your branch diverged from the main branch.

git rebase -i main

This command opens an editor showing a list of commits from the branch. Each line represents a commit and includes options for actions you can perform on each commit.

Step 2: Choose Your Actions

The editor will show commands like pick, reword, edit, squash, and drop next to each commit. Here’s what each command does:

• pick: Keep the commit as-is (default).
• reword: Edit the commit message without changing the content.
• edit: Make changes to the commit content.
• squash: Combine this commit with the previous one, merging both messages.
• drop: Remove the commit entirely.

For example, if you want to squash two commits together, change pick to squash for the second commit, and leave pick for the first.

Step 3: Save and Exit

After making your changes in the editor, save and close it. Git will proceed with the actions you specified, stopping if any conflicts arise. For each conflict, resolve it as described in the basic rebase steps.

Step 4: Confirm or Modify Commit Messages

If you used squash or reword, Git may prompt you to modify or confirm the combined commit message. Update the message as desired, then save and close the editor to complete the rebase.

Pushing a Rebasing Branch to a Remote Repository

If you’ve rebased a branch that is already on a remote repository, pushing it will require using the --force option, as rebasing rewrites commit history. Use this carefully, especially on shared branches:

git push origin feature-branch --force

Note: Rebasing and force-pushing can disrupt others who have pulled the previous commit history, so communicate with your team if you’re using this on a shared branch.

Practical Tips for Using Rebase

1. Use Rebase for Local Branches: Rebase is ideal for tidying up local branches before merging or pushing. Avoid rebasing public branches unless you’re sure it won’t interfere with others.
2. Keep a Backup: If you’re doing complex rebases, consider creating a backup branch in case anything goes wrong.
3. Use Interactive Rebase for Cleanup: Interactive rebase is excellent for combining commits, rewriting messages, and refining commit history.

When to Avoid Rebase

Rebasing is powerful, but there are cases where it’s best to use merge instead:

• On Public/Shared Branches: Avoid rewriting history on branches other team members are working on.
• Complex Merge Histories: For very complex histories, a merge may be simpler and clearer than attempting a rebase.
• Frequent Conflict Areas: If your rebase would involve multiple conflicts with the main branch, consider a merge to save time and avoid issues.

Conclusion

Git rebase is an excellent tool for maintaining a clean, linear history in your projects, especially when working with feature branches. Understanding when and how to use rebase—and the benefits it provides over merging—can greatly enhance the readability and manageability of your Git commit history. With this guide, you can start using rebase effectively to streamline your workflow, keep a clean project history, and manage version control with greater precision.