Git Rebase -i: Clean Up Commits Like a Pro (Day 1/30)

Welcome to Day 1 of our 30-day Git adventure! Today, we’re diving deep into one of Git’s most powerful and often misunderstood tools: interactive rebase, or git rebase -i. This isn’t just about rewriting history; it’s about crafting a clean, understandable commit history that makes collaboration and debugging a breeze. Think of it as the Marie Kondo of Git – sparking joy by eliminating clutter and making your codebase shine.

Why Bother Cleaning Up Your Commit History?

Before we jump into the technical details, let’s understand *why* cleaning up your commit history is so important. It’s not just about aesthetics; it significantly impacts your workflow and your team’s ability to work effectively.

1. Improved Code Review: A clean commit history tells a story. Reviewers can easily follow the logical steps you took to solve a problem, making the review process faster and more accurate. Small, focused commits make it easier to identify potential issues.
2. Easier Debugging: When bugs inevitably arise, a well-structured commit history makes it much easier to pinpoint the exact commit that introduced the problem using tools like git bisect. Imagine trying to find a needle in a haystack versus a needle in a neatly organized drawer.
3. Better Collaboration: When multiple developers contribute to a project, a clean commit history helps to maintain consistency and avoid conflicts. It provides a clear timeline of changes, making it easier for team members to understand each other’s work.
4. Professionalism: A clean commit history reflects a commitment to quality and attention to detail. It shows that you care about the long-term maintainability of the codebase. It’s a signal that you’re a responsible and collaborative developer.
5. Simplified Project Understanding: New developers joining the project will have an easier time understanding the project’s evolution and the reasoning behind specific code changes.

What is Git Rebase -i?

git rebase -i (interactive rebase) allows you to rewrite your commit history by providing a script of instructions to Git. You can:

• Reorder commits: Change the order in which commits were made.
• Squash commits: Combine multiple commits into a single, more meaningful commit.
• Edit commit messages: Correct typos, improve clarity, or add more context.
• Split commits: Divide a large commit into smaller, more focused commits.
• Drop commits: Remove commits that are no longer needed or contain errors.

Think of it as having a time machine for your Git history. You can go back, tweak things, and come back with a cleaner, more organized version of the past.

Prerequisites

Before we start, make sure you have a basic understanding of Git concepts like:

• Commits
• Branches
• The staging area (index)
• Basic Git commands (git add, git commit, git push, git pull, git branch, git checkout)

You should also have Git installed on your system. If not, you can download it from git-scm.com.

The Anatomy of a `git rebase -i` Session

Let’s walk through a typical git rebase -i session. We’ll start with a simple example and then move on to more complex scenarios.

Step 1: Identify the Range of Commits

The first step is to identify the range of commits you want to rebase. You can do this using the git log command.

For example, let’s say you have the following commit history:

    
        * commit c3d4e5f (HEAD -> feature/my-new-feature) Add initial styling
        * commit a1b2c3d Implement user authentication
        * commit e4f5a6b Fix minor bug in login form
        * commit 789abc0 Initial commit
    
    

You want to rebase the last three commits (a1b2c3d, e4f5a6b, and c3d4e5f) on top of the 789abc0 (initial commit).

Step 2: Initiate the Interactive Rebase

To start the interactive rebase, use the following command:

    
    git rebase -i 789abc0
    
    

Here, 789abc0 is the commit *before* the first commit you want to include in the rebase. Git will then present you with a text editor (usually your system’s default editor) containing a list of commits to be rebased.

Step 3: The Rebase Todo List

The text editor will display something similar to this:

    
    pick a1b2c3d Implement user authentication
    pick e4f5a6b Fix minor bug in login form
    pick c3d4e5f Add initial styling

    # Rebase 789abc0..c3d4e5f onto 789abc0
    #
    # Commands:
    # p, pick = use commit
    # r, reword = use commit, but edit the commit message
    # e, edit = use commit, but stop for amending
    # s, squash = use commit, but meld into previous commit
    # f, fixup = like "squash", but discard this commit's log message
    # x, exec = run command (the rest of the line) using shell
    # d, drop = remove commit
    #
    # These lines can be re-ordered; they are executed from top to bottom.
    #
    # If you remove a line here THAT COMMIT WILL BE LOST.
    #
    #       However, if you remove everything, you'll abort the rebase.
    #
    # Note that empty commits are commented out
    
    

This is the heart of the interactive rebase. Each line represents a commit that will be rebased. The first word on each line is a command that tells Git what to do with that commit.

The most common commands are:

• pick (or p): Use the commit as is. This is the default.
• reword (or r): Use the commit, but allow you to edit the commit message.
• edit (or e): Use the commit, but stop and allow you to amend the commit (add, remove, or modify files).
• squash (or s): Use the commit, but merge it into the previous commit. You’ll be prompted to edit the commit message of the combined commit.
• fixup (or f): Similar to squash, but discard the commit message of the squashed commit. The previous commit’s message will be used.
• drop (or d): Remove the commit entirely.

The order of the lines is significant. Commits are replayed in the order they appear in the file.

Step 4: Modify the Todo List

Now, let’s say you want to:

1. Reword the commit message of “Implement user authentication” to “Implement User Authentication System”.
2. Squash the “Fix minor bug in login form” commit into the “Implement User Authentication System” commit.
3. Leave the “Add initial styling” commit as is.

You would modify the todo list to look like this:

    
    reword a1b2c3d Implement user authentication
    squash e4f5a6b Fix minor bug in login form
    pick c3d4e5f Add initial styling
    
    

Save the file and close the editor. Git will then start the rebase process.

Step 5: Editing Commit Messages (if necessary)

Since you chose to reword the first commit, Git will open another editor window, allowing you to edit the commit message.

    
    Implement user authentication

    # Please enter the commit message for your changes. Lines starting
    # with '#' will be ignored, and an empty message aborts the commit.
    #
    # Date:      Mon Oct 23 10:00:00 2023 -0700
    #
    # interactive rebase in progress; onto 789abc0
    # Last command done (1 command done):
    #    reword a1b2c3d Implement user authentication
    # Next command to do (2 remaining commands):
    #    squash e4f5a6b Fix minor bug in login form
    # You are currently editing a commit during an interactive rebase.
    #   If you commit the current change, Git will continue the rebase
    #   immediately.
    
    

Change the message to “Implement User Authentication System” and save the file.

Step 6: Handling Squashed Commit Messages (if necessary)

Because you chose to squash the “Fix minor bug in login form” commit, Git will now open another editor window, allowing you to combine the commit messages of the two squashed commits.

    
    # This is a combination of two commits.
    # This is the 1st commit message:

    Implement User Authentication System

    # This is the commit message #2:

    Fix minor bug in login form

    # Please enter the commit message for your changes. Lines starting
    # with '#' will be ignored, and an empty message aborts the commit.
    #
    # Date:      Mon Oct 23 10:00:00 2023 -0700
    #
    # interactive rebase in progress; onto 789abc0
    # Last command done (2 commands done):
    #    squash e4f5a6b Fix minor bug in login form
    # Next command to do (1 remaining commands):
    #    pick c3d4e5f Add initial styling
    # You are currently editing a commit during an interactive rebase.
    #   If you commit the current change, Git will continue the rebase
    #   immediately.
    
    

You can edit this message to create a cohesive description of the combined changes. For example, you could change it to:

    
    Implement User Authentication System and fix a minor bug in the login form.
    
    

Save the file.

Step 7: Completing the Rebase

Git will continue replaying the remaining commits in the todo list. In this case, it will apply the “Add initial styling” commit without any further intervention.

If the rebase is successful, you’ll see a message like this:

    
    Successfully rebased and updated refs/heads/feature/my-new-feature.
    
    

Step 8: Verifying the Result

Use git log to verify that the commit history has been updated as expected.

    
        * commit f123a4b (HEAD -> feature/my-new-feature) Add initial styling
        * commit 987b65c Implement User Authentication System and fix a minor bug in the login form.
        * commit 789abc0 Initial commit
    
    

Notice that the “Implement user authentication” and “Fix minor bug in login form” commits have been squashed into a single commit, and the commit message has been updated.

Common Rebase Commands in Detail

Let’s take a closer look at each of the common rebase commands:

`pick` (p) – Use the commit

This is the simplest command. It tells Git to use the commit as is, without any modifications. The commit will be replayed on top of the new base.

`reword` (r) – Edit the commit message

This command allows you to change the commit message. This is useful for correcting typos, adding more context, or improving the overall clarity of the commit message. Git will pause during the rebase process and open an editor window, allowing you to modify the commit message.

`edit` (e) – Amend the commit

This is the most powerful (and potentially dangerous) command. It allows you to modify the commit itself, including the files it changes. Git will pause the rebase process and allow you to stage new changes, modify existing changes, or even remove changes from the commit. After making your changes, you need to use git commit --amend --no-edit to update the commit. The --no-edit flag tells Git to keep the original commit message. If you want to change the commit message as well, omit the --no-edit flag.

`squash` (s) – Merge into the previous commit

This command combines the current commit with the previous commit. Git will pause the rebase process and allow you to edit the commit message of the combined commit. This is useful for combining small, related commits into a single, more meaningful commit.

`fixup` (f) – Merge into the previous commit, discard message

This command is similar to squash, but it discards the commit message of the squashed commit. The commit message of the previous commit will be used. This is useful for squashing commits that contain minor fixes or adjustments that don’t warrant their own commit message.

`drop` (d) – Remove the commit

This command removes the commit entirely. The changes introduced by the commit will be lost. This is useful for removing commits that contain errors, are no longer needed, or were created accidentally.

Real-World Examples

Let’s look at some more real-world examples of how you can use git rebase -i to clean up your commit history.

Example 1: Combining Several Small Fixes

You’ve been working on a new feature and have made several small commits to fix minor issues. Your commit history looks like this:

    
        * commit 1234567 (HEAD -> feature/my-feature) Implement feature X
        * commit 2345678 Fix typo in function name
        * commit 3456789 Add missing semicolon
        * commit 4567890 Correct indentation
        * commit 5678901 Initial commit
    
    

You want to combine the typo fix, missing semicolon, and indentation correction into a single commit.

Run git rebase -i 5678901 and modify the todo list like this:

    
    pick 1234567 Implement feature X
    fixup 2345678 Fix typo in function name
    fixup 3456789 Add missing semicolon
    fixup 4567890 Correct indentation
    
    

This will combine the three fixup commits into the “Implement feature X” commit, using its commit message.

Example 2: Splitting a Large Commit

You made a large commit that includes several unrelated changes. Your commit history looks like this:

    
        * commit abcdef0 (HEAD -> feature/my-feature) Implement feature Y (includes multiple unrelated changes)
        * commit fedcba9 Initial commit
    
    

You want to split this commit into smaller, more focused commits.

Run git rebase -i fedcba9 and modify the todo list like this:

    
    edit abcdef0 Implement feature Y (includes multiple unrelated changes)
    
    

Git will pause at the abcdef0 commit. Now, you need to:

1. Reset the commit: git reset HEAD^ (This moves the changes from the commit back into the staging area).
2. Stage and commit the first set of changes: git add ; git commit -m "Implement first part of feature Y"
3. Stage and commit the second set of changes: git add ; git commit -m "Implement second part of feature Y"
4. Continue the rebase: git rebase --continue

This will split the original commit into two smaller, more focused commits.

Example 3: Removing a Bad Commit

You accidentally committed a file containing sensitive information, such as a password or API key. Your commit history looks like this:

    
        * commit ghi7890 (HEAD -> feature/my-feature) Add sensitive information
        * commit jkl8901 Implement feature Z
        * commit mno9012 Initial commit
    
    

You need to remove the commit containing the sensitive information.

Run git rebase -i mno9012 and modify the todo list like this:

    
    drop ghi7890 Add sensitive information
    pick jkl8901 Implement feature Z
    
    

This will remove the ghi7890 commit. Warning: This will permanently remove the commit and its changes from your history. If you’ve already pushed this commit to a remote repository, you’ll need to force-push your changes (more on that later, but be careful!). Also, consider rotating any compromised credentials.

Best Practices for Using `git rebase -i`

To use git rebase -i effectively and avoid potential problems, follow these best practices:

1. Rebase Only Your Local Branches: Never rebase branches that are shared with others (e.g., the main or develop branch). Rebase is a destructive operation that rewrites history, and rewriting shared history can cause significant problems for other developers.
2. Communicate with Your Team: If you must rebase a shared branch (which is generally discouraged), communicate with your team beforehand to ensure that everyone is aware of the changes and knows how to handle them.
3. Don’t Rebase After Pushing: Avoid rebasing commits that have already been pushed to a remote repository. If you do, you’ll need to force-push your changes, which can overwrite the history of the remote repository and cause problems for other developers. This is especially true if others have based their work on those pushed commits.
4. Keep Commits Small and Focused: When creating new commits, try to keep them small and focused on a single logical change. This will make it easier to rebase and clean up your history later.
5. Write Clear and Concise Commit Messages: Write commit messages that clearly describe the changes you made. This will make it easier for others (and your future self) to understand your work. Use the imperative mood (“Fix bug” instead of “Fixed bug” or “Fixes bug”).
6. Use a Visual Git Tool: Tools like GitKraken, Sourcetree, or GitExtensions can make interactive rebasing easier by providing a visual interface for managing your commits and branches.
7. Back Up Your Branch Before Rebasing: Create a backup of your branch before starting a rebase. This will allow you to easily revert to the original state if something goes wrong. You can do this with: git branch backup-my-branch
8. Test Thoroughly After Rebasing: After rebasing, test your code thoroughly to ensure that the changes were applied correctly and that no new issues were introduced.

Potential Problems and How to Handle Them

While git rebase -i is a powerful tool, it can also lead to problems if used incorrectly. Here are some common issues and how to handle them:

Conflicts

Conflicts can occur during a rebase if the changes you’re trying to apply conflict with existing changes in the codebase. Git will pause the rebase process and ask you to resolve the conflicts manually.

To resolve conflicts:

1. Identify the conflicting files: Git will mark the conflicting files in your working directory.
2. Open the conflicting files: Use a text editor or a merge tool to open the conflicting files.
3. Resolve the conflicts: Edit the files to resolve the conflicts. Git will insert conflict markers (<<<<<<< HEAD, =======, >>>>>>>>> branch-name) to indicate the conflicting sections. Remove the conflict markers and make the necessary changes to reconcile the differences.
4. Stage the resolved files: git add
5. Continue the rebase: git rebase --continue

Losing Commits

It’s possible to lose commits during a rebase if you accidentally drop them or make a mistake in the todo list. That’s why backing up your branch beforehand is crucial.

If you lose commits, you can try to recover them using git reflog. The reflog is a record of all the changes that have been made to your repository. You can use it to find the lost commits and restore them to your branch.

Force-Pushing

If you rebase commits that have already been pushed to a remote repository, you’ll need to force-push your changes to overwrite the history of the remote repository. Force-pushing should be done with extreme caution, as it can cause problems for other developers who are working on the same branch.

To force-push your changes:

    
    git push --force origin 
    
    

Before force-pushing, make sure you understand the implications and communicate with your team. If possible, avoid rebasing shared branches altogether.

Conclusion

git rebase -i is a powerful tool for cleaning up your commit history and making your codebase more maintainable. By mastering this technique, you can become a more effective and collaborative developer. Remember to practice on local branches first, understand the commands thoroughly, and always back up your work before rebasing.

Tomorrow, we’ll delve into more advanced rebase scenarios and explore techniques for handling complex commit histories. Stay tuned for Day 2!