Git Rebase Tutorial

Beginners of Git are warned against the rebase command. And rightfully so. With all the new things to learn, beginners are probably better off mastering the basic concepts before delving into the intricacies of rebasing. However, if you understand the basics of merging branches, then knowing how to rebase can help you solve some complicated development puzzles when the right time comes.

Git Rebase: Definitions

According to the git documentation, the rebase command will reapply commits on top of another base tip. This definition might be a little daunting. It’s easier to explain rebase as a procedure that adds the changes of the current branch to the tail of another branch. Let’s walk through an example to get a better idea of what happens.

Git Rebasing Example

In this example, we will first create a test case with ‘master’ and ‘feature’ branch. Then we will do a standard merge. Next, we will recreate the test case and perform rebase and merge.

1. Creating Master and Feature Branches

Here is the scenario we will create:

In the above example, we are taking the following path:

1. Commit A: we add a.txt file in the ‘master’ branch

2. Commit B: we add b.txt file in the ‘master’ branch

3. At this stage, we create the branch ‘feature’ which means it will have a.txt and b.txt

4. Commit C: we add c.txt file in the ‘master’ branch

5. We go to the ‘feature’ branch

6. Commit E: we modify a.txt in ‘feature’ branch

7. Commit F: we modify b.txt in ‘feature’ branch

You can create a folder and run the following code inside the folder to create the above situation:

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2. Simple Merge

Let’s use the log command to check both branches.

Results for ‘master’:

Results for ‘feature’:

Notice how the feature branch does not have Commit C

Now let’s run merge ‘feature’ branch with ‘master’ branch. You will be asked to enter a comment. In the comment, add “Commit G:” at the beginning to make it easier to track.

Results for ‘master’:

Results for ‘feature’:

In the ‘master’ branch, you will notice there is a new commit G that has merged the changes from ‘feature’ branch. Basically, the following action has taken place:

In the Commit G, all the changes from ‘feature’ branch have been brought into the master branch. But the ‘feature’ branch itself has remained untouched due to the merge process. Notice the hash of each commit. After the merge, E (7c5c85e) and F (0286690) commit has the same hash on the ‘feature’ and ‘master’ branch.

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3. Merging with Rebasing

Let’s repeat step 1 to create the ‘master’ and ‘feature’ branches again.

Results for ‘master’:

Results for ‘feature’:

Let’s rebase from the ‘feature’ branch.

Then merge ‘feature’ into ‘master’.

Results for ‘master’ branch:

Results for ‘feature’ branch:

Notice that after the rebase and merge both branches are the same. Also, the hashes for E and F have changed in both branches. Basically, in the rebase scenario, this is what happened:

That’s why there is no new commit. The E and F commits have been recalculated and latched to the end of the ‘master’ branch.

Rebasing is a useful tool when you want to clean up the history of your work. However, there is a danger which has given birth to the golden rule.

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Golden Rule of Rebasing

The golden rule of rebasing is :

Never rebase a public branch.

As you can see from the example above, rebasing recalculates the commits. When multiple people are branching from a public repository, rebasing can create situations where developers who have created new branches will run into very complicated merge situations. So, it’s a good idea never to rebase public branches that are shared.

In Conclusion:

Rebasing is a unique feature of Git. But use it with caution.

More Information:

Here are some links for further study:

Git Rebase Documentation
Atlassian Merging vs Rebasing

References:

• https://www.atlassian.com/git/tutorials/merging-vs-rebasing
• Version Control with Git – 07 – Rebase [https://www.youtube.com/watch?v=cSf8cO0WB4o]
• https://git-scm.com/docs/git-rebase
• What is Git rebase? [https://www.youtube.com/watch?v=TymF3DpidJ8]
• https://medium.freecodecamp.org/git-rebase-and-the-golden-rule-explained-70715eccc372