Rebase itself has 2 main modes: “manual” and “interactive” mode.
What is git rebase?
Rebasing is the process of moving or combining a sequence of commits to a new base commit. Rebasing is most useful and easily visualized in the context of a feature branching workflow. The general process can be visualized as the following:
From a content perspective, rebasing is changing the base of your branch from one commit to another making it appear as if you’d created your branch from a different commit. Internally, Git accomplishes this by creating new commits and applying them to the specified base. It’s very important to understand that even though the branch looks the same, it’s composed of entirely new commits.
Usage
The primary reason for rebasing is to maintain a linear project history.
For example, consider a situation where the main branch has progressed since you started working on a feature branch. You want to get the latest updates to the main branch in your feature branch, but you want to keep your branch’s history clean so it appears as if you’ve been working off the latest main branch. This gives the later benefit of a clean merge of your feature branch back into the main branch. Why do we want to maintain a “clean history”?
The benefits of having a clean history become tangible when performing Git operations to investigate the introduction of a regression. A more real-world scenario would be:
A bug is identified in the main branch. A feature that was working successfully is now broken. A developer examines the history of the main branch using git log because of the “clean history” the developer is quickly able to reason about the history of the project.
The developer can not identify when the bug was introduced using git log so the developer executes a git bisect. Because the git history is clean, git bisect has a refined set of commits to compare when looking for the regression. The developer quickly finds the commit that introduced the bug and is able to act accordingly. Learn more about git log and git bisect on their individual usage pages.
You have two options for integrating your feature into the main branch: merging directly or rebasing and then merging. The former option results in a 3-way merge and a merge commit, while the latter results in a fast-forward merge and a perfectly linear history. The following diagram demonstrates how rebasing onto the main branch facilitates a fast-forward merge.
Rebasing is a common way to integrate upstream changes into your local repository. Pulling in upstream changes with Git merge results in a superfluous merge commit every time you want to see how the project has progressed. On the other hand, rebasing is like saying, “I want to base my changes on what everybody has already done.”
Don’t rebase public history
As we’ve discussed previously in rewriting history, you should never rebase commits once they’ve been pushed to a public repository. The rebase would replace the old commits with new ones and it would look like that part of your project history abruptly vanished.