How to Use the Git Rebase Command

In Git, managing code history is important for tracking changes. For this purpose, git supports several commands, such as commit, log, diff, branch, merge, revert, and rebase. The git rebase command, in particular, is useful for keeping branch histories clean by allowing developers to reapply commits from one branch to another. In this article, we’ll discuss what git rebase is, how it differs from the git merge command, and how to use it to maintain a structured, linear commit history that’s easier to read and review.

Understanding Git Rebase: What Is It?

The git rebase command allows us to move, combine, reorder, edit, or remove commits. Moreover, it simplifies the project history by moving the commits of one branch onto the base of another branch. Rebase in git is especially useful when integrating changes into a feature branch, resulting in a streamlined history without unnecessary merge commits.

Git Rebase vs. Git Merge: What’s the Difference?

Both merge and rebase commands are used to combine branches, but they differ in how the commit history looks after one branch is added to another. Here’s a comparison to understand when to use rebase versus merge:

• Git Merge: It combines the histories of both branches and creates a merge commit, marking the point where they joined. This commit retains the complete history of both branches.

• Git Rebase: It applies changes from one branch to another and rewrites the history as though all work was done linearly.

Git Merge maintains separate histories for each branch, while Git Rebase linearizes the history, making it appear as if all work was done in a straight line. When using git merge, the focus is on merging feature branches, whereas git rebase is used to rewrite and clean up the commit history for better organization and readability.

Basic Syntax and Options for Git Rebase

The git rebase command allows users to transfer commits from the current branch to the base of another branch. The basic syntax of the git rebase command is shown below:

git rebase <target-branch>

Users can use different options with the git rebase command, which are listed below: 

• git rebase master: This command adds all the changes from the master branch to your current branch.
• -I or --interactive: This option opens an editor to reorder, combine, or modify commits interactively.
• --onto <newbase>: This option enables us to set a new base commit for the rebase. We can use it to move several commits to a different branch or commit.
• --skip: This option skips a commit if there's a conflict during rebase. It tells Git to ignore that commit and continue with the rebase.
• --no-verify: This option ignores any pre-commit checks set up in the repository. It’s useful if we want to commit quickly without running those checks.
• --auto-squash: It automatically applies the fixup or squash flags to commits. This is helpful for cleaning up commit history during an interactive rebase.

These git rebase options should be used carefully, as they can change the commit history of the repository. It is recommended to back up your code before running the rebase command in Git. This way, users can restore the original code if anything goes wrong.

How to Perform an Interactive Rebase

Interactive rebasing enables users to reorder, combine, or edit commit messages. This practice gives users precise control over their history. Go through the following steps to perform an interactive rebase:

Step 1: Switch to the feature branch

Users can use the git checkout command to navigate to a different branch in a Git repository:

git checkout <feature-branch>

This command changes the user's current working branch to the specified <feature-branch>. After switching, any subsequent Git operations, including rebase, will be performed in the context of that branch.

Step 2: Start interactive rebase

Users can run the rebase command with the -i option to perform an interactive rebase:

git rebase -i <target-branch>

When a user runs this command, it opens the default text editor. The user will see a list of commits from the current branch that are not present in <target-branch>. Each commit comes with actions to choose from, such as:

• pick: Keep the commit as it is.

• edit: Stop and allow changes to the commit (like the message or the files).

• squash: Combine this commit with the one before it.

• drop: Removes a commit. 

After the user makes the desired changes and saves the file, Git will continue the rebase based on the selected choices.

Handling Merge Conflicts During Rebase

When rebasing, conflicts can occur if the same line of code is modified in both branches. In that case, Git pauses the rebase process, allowing users to resolve conflicts. Follow the steps below to resolve the merge conflicts during the rebase:

Step 1: Identify Conflicting Files

Run the git status command to see where the problem/conflict lies in a Git repository:

git status

This command displays a list of files that have conflicts, marked as unmerged.

Step 2: Edit the Conflicted Files

When there are conflicts during a Git operation, like a merge or rebase, Git marks the conflicting parts in the files with special markers:

• <<<<<<< HEAD: It shows the user's changes (from the current branch).

• =======: It separates the user's changes from the other branch's changes.

• >>>>>>> <branch-name>: It shows the end of the conflicting section and shows the name of the branch with the conflicting changes.

To resolve the conflicts, users should open the files in a text editor and decide which changes to keep. They can choose to:

• Keep their changes.

• Keep the changes from the other branch.

• Combine both sets of changes.

After making the edits, it's important to remove the conflict markers to clean up the code and make sure it works properly.

Step 3: Stage the Resolved Files

Once conflicts have been resolved, the next step is to stage the resolved files. This is done using the following command:

git add <file-name>

Replace <file-name> with the file’s name that was edited. If multiple files are resolved, they can be added simultaneously or individually.

Step 4: Continue the Rebase

After staging the resolved files, users can continue the rebase process with the command:

git rebase --continue

How to Abort, Skip, or Continue a Rebase

Users can manage the rebase process by executing the git rebase command with the abort, skip, and continue options.

Aborting the Rebase

Run the git rebase command with the --abort option to cancel the ongoing rebase and return the branch to its original state:

git rebase --abort

Skipping the Rebase

Similarly, if a user runs into unresolved conflicts during a rebase, he can execute the git rebase command with the --skip option to omit the problematic commit:

git rebase --skip

Continuing the Rebase

If we encounter conflicts while rebasing, we need to resolve them first. After fixing the issues, we can run the rebase command with the --continue option to continue the rebasing process:

git rebase --continue

Common Mistakes

Users can encounter several issues during Git rebase, such as merge conflicts, uncommitted changes, aborted rebase attempts, etc. Here are some common mistakes that users may face while rebasing:

Merge Conflicts

Users can face merging conflicts when changes in the rebased branch overlap with the base branch. These conflicts require manual resolution. Use the git add <filename> command to mark conflicts as resolved. Then, continue with the git rebase --continue command.

Uncommitted Changes

If you have uncommitted changes in your working directory, Git won't allow a rebase. In that case, commit or stash your changes with git stash before starting the rebase.

Rebasing Shared Branches

Rebasing the shared branches can create confusion and conflicts. To avoid this issue, users can rebase the branches that they own or are not currently used by anyone else.

Complex History

A branch with a complicated commit history can make the rebase process error-prone. In such cases, consider using git merge instead or simplify the history before rebasing.

Incorrect Rebase Sequence

Specifying the wrong base commit can lead to unexpected changes. Therefore, it is recommended to always double-check that you are rebasing onto the correct branch.

Apart from this, the git rebase command has several disadvantages, including increased complexity compared to merging, especially with complex commit histories. It can lead to lost commits if the wrong branch is rebased or if conflicts are unresolved. Additionally, rebasing alters the commit history in public repositories, which makes collaboration difficult.

Conclusion

In Git, the rebase command helps maintain a clean and readable commit history. However, it requires careful usage due to certain challenges. Therefore, before making significant changes to a branch’s commit history, it’s important to carefully consider the risks and benefits of using the git rebase command.