Understanding Git Rebase

Git provides a multitude of ways to manage changes and development paths, one of which is the git rebase command. This command is a powerful tool that can make your commit history cleaner, resolve conflicts in a more controlled manner, and help you navigate through the complex waters of collaborative development.

To better visualize and understand the concept, let’s consider the following diagram:

graph LR
    A[Initial Commit] --> B[Commit 2]
    B --> C[Commit 3]
    C --> D[Commit 4]
    B --> E[Commit 5 on Feature Branch]

In this diagram, we have a main branch with commits up to Commit 4, and a feature branch diverging from Commit 2 with Commit 5.

Why use git rebase?

The primary reason to use git rebase is to maintain a linear project history. Without rebasing, your project’s history can become scattered with a multitude of separate branch timelines, which can make understanding the flow of the project difficult. By using git rebase, you can ensure that commits apply directly to the tip of the chosen branch, keeping your project history neat and readable.

Rebasing is also useful when you want to modify older or multiple commit messages, combine commits, or delete unnecessary commits.

What does git rebase do?

The git rebase command moves or combines commits to a new base commit. It’s like saying, “I want to base my changes on what everyone else has already done.”

Here’s what happens under the hood:

Git pauses whatever you are doing on your branch.
It takes your changes and saves them outside your repository.
Git switches to the branch you are rebasing onto.
It applies your changes one by one to this branch.

This process can be visualized as follows:

sequenceDiagram
    participant Git
    participant Your Branch
    participant Base Branch
    Git->>Your Branch: Pause and save changes
    Git->>Base Branch: Switch and apply changes

This process can result in conflicts if changes on the branch you’re rebasing onto overlap with your changes. Git will pause and allow you to resolve the conflicts manually. Once you’ve resolved conflicts, you can continue the rebase process.

How to use git rebase?

Suppose you have a feature branch that you’ve worked on, and you want to rebase it onto the main branch. The command you would use is:

git checkout feature
git rebase main

This moves your entire feature branch to begin on the tip of the main branch, effectively incorporating all of the new commits in main. But, instead of using a merge commit, rebasing re-writes the project history by creating brand new commits for each commit in the original branch.

The diagram below illustrates this concept:

graph LR
    A[Initial Commit] --> B[Commit 2]
    B --> C[Commit 3]
    C --> D[Commit 4]
    D --> E[Commit 5 on Feature Branch - After Rebase]

Interactive rebasing

Interactive rebasing gives you even more power by allowing you to alter individual commits in the process. This is done by providing the -i option to git rebase.

git rebase -i HEAD~3

This command will open a text editor with a list of the last 3 commits on the current branch, and a set of commands to perform on each commit. These commands include:

pick: use commit
reword: use commit, but edit the commit message
edit: use commit, but stop for amending
squash: use commit, but meld into previous commit
fixup: like “squash”, but discard this commit’s log message
exec: run command (the rest of the line) using shell

You can rearrange the commits in this list to change the commit order. Git will reapply the commits in the new order.

When not to use git rebase?

While git rebase has many benefits, it’s not always the right tool for the job. If you’ve shared your commits with others, you shouldn’t rebase your commits. Rebase will create new commits that others won’t have in their repository. This can lead to conflicts and confusion among your collaborators.

In short, git rebase is a powerful command that can help make your commit history cleaner and more understandable, help resolve conflicts in a more controlled manner, and aid in navigating the complex terrain of collaborative development. However, like any tool, it should be used judiciously and appropriately.

Remember, always use git rebase responsibly.