Understanding Git Rebase - Developer Community Blog

In the world of software development, version control systems are indispensable. Git, being the most popular one, offers a plethora of commands and workflows to manage code effectively. Among these, git rebase stands out as a powerful tool, often discussed and sometimes misunderstood. This post aims to demystify git rebase, explaining what it is, why you should use it, and how to use it safely.

What is Git Rebase?

At its core, git rebase is a command that allows you to move or combine a sequence of commits to a new base commit. Instead of merging two branches, which creates a merge commit, rebase rewrites the commit history by reapplying commits from one branch onto another. Think of it as transplanting a series of changes from one point in the history to another.

Visualizing the change in commit history after rebasing.

Consider this scenario: You're working on a feature branch (`feature`) that has diverged from the main branch (`main`). While you've been working, new commits have been added to `main`. If you were to merge `main` into `feature` now, you'd get a merge commit that clutters your history. Rebasing `feature` onto `main` instead rewrites `feature`'s history to appear as if it was created after the latest commit on `main`.

Why Use Git Rebase?

The primary benefit of rebasing is maintaining a clean, linear project history. This makes it easier to:

Understand the project's evolution: A linear history without unnecessary merge commits is much easier to read and follow.
Debug issues: When looking for the commit that introduced a bug, a clean history simplifies the process of `git bisect`.
Simplify collaboration: Smaller, focused commits that are rebased onto the latest main branch changes are easier for teammates to review and integrate.

Rebasing can also be used for interactive rebasing, which offers more granular control:

--interactive or -i: Allows you to reorder, edit, squash (combine), or drop commits.

How to Use Git Rebase

Let's walk through a common workflow. Suppose you have a branch named `my-feature` that you branched off `main`. While you're working, new commits are added to `main`.

1. Update your local main branch:

git checkout main
git pull origin main

2. Rebase your feature branch onto the updated main:

git checkout my-feature
git rebase main

At this point, Git will take each commit from `my-feature` and try to reapply it on top of the latest commit from `main`. If there are no conflicts, your `my-feature` branch will now be based on the latest `main`.

                Important Note: Rebasing rewrites commit history. Never rebase commits that have already been pushed to a shared remote repository if others might have based their work on those original commits. This can lead to a messy and confusing history for your collaborators. The golden rule is: Do not rebase public history.
            

Handling Conflicts During Rebase

If Git encounters conflicts (i.e., changes in your branch and the base branch modify the same lines of code), the rebase process will pause:

Git will inform you about the conflicting files.
Manually edit the conflicting files to resolve the differences.
Stage the resolved files: git add <conflicted-file>
Continue the rebase: git rebase --continue

If you get stuck or want to abort the rebase, you can always run:

git rebase --abort

Interactive Rebase: Cleaning Up Your Local Commits

Interactive rebase (git rebase -i) is incredibly useful for cleaning up your commits before you push them. It allows you to:

pick: Use the commit as is.
reword: Use the commit, but edit the commit message.
edit: Use the commit, but stop for amending.
squash: Use the commit, but meld it into the previous commit.
fixup: Like "squash", but discard this commit's log message.
drop: Remove the commit entirely.

To use it, specify the number of commits you want to modify (e.g., the last 3 commits):

git rebase -i HEAD~3

This will open an editor with a list of your last three commits. You can then change the command next to each commit as needed.

Rebase vs. Merge

It's crucial to understand the difference:

Merge: Preserves history exactly as it happened, creating a merge commit to join branches. History is non-linear.
Rebase: Rewrites history to create a linear progression, making it appear as if commits were made sequentially. History is linear.

Choose rebase for cleaning up local history and integrating changes from a base branch into your feature branch to keep it up-to-date. Use merge when you want to preserve the exact branching history or when integrating branches that have been shared publicly.

Conclusion

git rebase is a powerful tool for maintaining a clean and understandable Git history. By understanding its mechanics and the difference between rebasing and merging, you can significantly improve your development workflow and make collaboration smoother. Remember the golden rule: rebase only your local, unpushed commits.

Happy coding!