Scared of git pull --rebase? Rebase with Confidence


GIT

Introduction to git pull --rebase

Git is a distributed version control system where multiple developers can work on a project simultaneously. This often leads to situations where multiple developers have made changes to the same codebase in parallel. To integrate these changes into a single line of development, Git provides various strategies, one of which is rebase. The command git pull --rebase is a combination of git pull and git rebase commands and provides a mechanism to update your local branch while preserving a linear commit history.

What does it do?

When you execute git pull --rebase, Git performs the following steps:

  • Fetch Changes: It fetches commits from the remote branch that don't exist in your current branch.
  • Replay Commits: It then temporarily saves your new commits (those that aren't in the remote branch) and applies the fetched commits to your branch.
  • Reapply Your Commits: Finally, Git reapplies your saved commits on top of your branch one by one.

The result is a linear commit history, where your new commits appear to have been made directly on top of the fetched commits, as if no parallel development had occurred.

Why use git pull --rebase over the default pull?

Using git pull --rebase instead of the default git pull (which is essentially git pull --merge) has several benefits:

  • Cleaner History: Rebasing results in a linear commit history without merge commits (which get introduced when there's parallel development). This makes the history easier to read and understand.
  • Easier Debugging: Linear commit history simplifies debugging using tools like git bisect.
  • Avoid Merge Commits: Some teams prefer to avoid merge commits for minor parallel developments, as they can clutter the history with "Merge branch" messages.
  • Code Review: It can make code review processes simpler because changes are presented as if they were developed sequentially.
  • Conflict Resolution: While conflicts can arise with both merging and rebasing, with rebasing, you handle conflicts commit-by-commit, which might make it clearer to understand the context of the conflict.

However, it's essential to note that git pull --rebase has its caveats:

  • Rewriting History: Rebasing rewrites commit history, which can be problematic if you're working on a public branch with other collaborators. They would have to perform additional steps to synchronize their local branches.
  • Learning Curve: For newcomers to Git, rebasing can initially seem more complex than merging.

 

Step-by-Step Workflow with git pull --rebase

Let us understand the workflow of git pull --rebase using following scenario:

1. Priya creates a topic branch, topic-branch-P, and starts working on her features or fixes.

2. Rohan creates an unrelated topic branch, topic-branch-R, and begins working on his own set of features or fixes.

3. Priya checks out the master branch and tries to pull any new changes:

Priya:~$ git checkout master
Priya:~$ git pull

She receives the message: Master is already up to date.

4. Rohan does the same as Priya:

Rohan:~$ git checkout master
Rohan:~$ git pull

He also gets the message: Master is already up to date.

5. Priya merges her topic branch into the master:

Priya:~$ git merge topic-branch-P

6. Similarly, Rohan merges his topic branch into the master:

Rohan:~$ git merge topic-branch-R

7. Rohan pushes his changes to the remote master before Priya does:

Rohan:~$ git push origin master

8. Priya tries to push her changes, but her push is rejected because Rohan's commits are in the remote master, and her push is not a fast-forward merge:

Priya:~$ git push origin master

She receives a rejection message.

9. Priya checks the commit log of origin/master:

Priya:~$ git log origin/master

She observes Rohan's commit and realizes it's unrelated to her changes.

10. Priya decides to use git pull --rebase to integrate her changes:

Priya:~$ git pull --rebase origin master

During this process, Priya's merge commit is unwound, Rohan's commit is pulled in, and Priya's changes are applied sequentially after Rohan's commit.

11. Priya then pushes her changes to the remote master:

Priya:~$ git push origin master

 

When to use and when not to use git pull --rebase ?

The difference between git pull (which defaults to a merge strategy) and git pull --rebase (rebase strategy) affects how changes from different branches get integrated, and how the commit history appears afterward. Both approaches have their merits and drawbacks, and understanding them helps to decide which one is more appropriate for a given situation.

 

git pull (Merge Strategy)

How it works:

  • When you run git pull, it fetches the changes from the remote repository and then merges those changes into your current branch.
  • If both you and someone else have committed changes, git pull will create a new "merge commit" to join the two lines of development.
Scared of git pull --rebase? Rebase with Confidence

Why you might use it:

  • Commit History Integrity: It preserves the exact history of commits, showing explicitly when and where a merge occurred.
  • Simplicity: It's generally more straightforward for Git beginners, especially when working with shared, public branches. There's no risk of rewriting public commit history.

Drawbacks:

  • Cluttered Log: Over time, especially in active projects, the history can become cluttered with many merge commits, making it harder to read.
  • Lack of Linear History: As multiple branches are merged into master/main, it can be challenging to trace the development history of a particular feature or fix.

 

git pull --rebase (Rebase Strategy)

How it works:

  • Instead of merging the remote branch's changes into yours, it "replays" your local commits on top of the latest commit from the remote branch.
  • This effectively rewrites your branch's commit history, making it appear as if your changes happened after all the changes from the remote branch.
Scared of git pull --rebase? Rebase with Confidence

Why you might use it:

  • Linear Commit History: It maintains a clean, linear commit history without additional merge commits.
  • Easier History Tracing: With a linear history, it's easier to use tools like git bisect and understand the order of changes.
  • Simplifies Code Review: A linear commit sequence can be easier to review and understand, especially when integrating a feature branch back into the mainline.
  • Conflict Handling: With rebasing, if there are conflicts, they are presented one at a time as Git tries to apply each commit. This can sometimes make conflict resolution more contextual and manageable.

Drawbacks:

  • Rewrites Commit History: This can be problematic in shared branches. If multiple users are working on the same branch and one user rebases the branch, other users will face challenges when trying to push their changes.
  • Complexity for Beginners: Rebasing can seem more complex and intimidating, especially for those new to Git.

 

Deep Dive into Advanced Topics

The deeper you dive into Git, the more powerful tools and techniques you'll discover that can help manage and clean up your project's history. Here are explanations of some advanced topics:

 

1. git rebase --onto: Rebasing onto Another Branch

Sometimes, you may find yourself in a situation where you've based your branch on one branch, but then decide it should be based on a different branch. This can be accomplished using the --onto flag with git rebase.

Scenario: Suppose you have three branches: featureA, featureB, and master. You started featureB based on featureA, but now you realize featureB should be based on master.

How to use:

git checkout featureB
git rebase --onto master featureA featureB

Here's what happens:

  • The first argument after --onto (master) is where you want to base your branch.
  • The second argument (featureA) is where your branch currently starts.
  • The last argument (featureB) is the branch you're rebasing.

This command tells Git to rebase the featureB branch onto master, starting from where it diverged from featureA.

 

2. Using Autosquash with Interactive Rebasing

Interactive rebasing is an incredibly powerful tool that allows you to modify commits as you move them. When you use the --autosquash flag, Git will automatically recognize and apply commits that you've marked for squashing or fixing up.

How to use:

When committing changes that you intend to squash or fix-up into another commit, use the --squash or --fixup flags:

git commit --fixup=<SHA-of-commit-to-be-fixed>

OR

git commit --squash=<SHA-of-commit-to-be-fixed>

Then, during an interactive rebase:

git rebase -i --autosquash <base-commit-SHA>

Git will automatically arrange the commits in the correct order and mark them for squashing or fixing up.

 

3. Squashing Commits

Over time, you might end up with a series of small commits that would be more understandable if they were combined into a single, well-described commit. Squashing commits helps in achieving this.

How to use:

Start an interactive rebase for the last n commits:

git rebase -i HEAD~n

In the text editor that opens, you'll see a list of commits. At the start of each line, you'll see the word pick.

To squash a commit into the previous one, replace pick with squash or s. If you want to squash the commit and discard its commit message, use fixup or f.

After saving and closing the editor, if you've chosen squash, you'll have an opportunity to edit the combined commit message. Make your changes, save, and close the editor.

Once done, the specified commits will be squashed into a single commit.

Note: Squashing and other history-rewriting actions should be used cautiously on shared/public branches, as they change commit SHAs and can cause confusion for other collaborators.

 

Frequently Asked Questions

What is the difference between merging and rebasing?

Merging takes the contents of a source branch and integrates them with a target branch. This creates a new commit in the target branch that has two parent commits.
Rebasing takes a set of commits, "copies" them, and applies them onto another branch. It's like reapplying your work on top of another base.

When should I use git pull vs. git pull --rebase?

Use git pull (which merges) when you want to preserve the exact history of your branch, including when and where it branched from the mainline.
Use git pull --rebase when you want a cleaner, linear history.

Can rebasing be dangerous?

Yes, especially on shared branches. Rebasing rewrites commit history, which can cause conflicts and confusion for other collaborators if used on branches they're also working on. Always coordinate with your team when rebasing shared branches.

I just rebased, but now I can't push. Why?

After a rebase, your local branch and the remote branch diverge because they have different commit histories. Use git push origin <branch-name> --force-with-lease to push after rebasing. The --force-with-lease option is a safer way to force-push as it checks the remote branch for changes before pushing.

What is git rebase --onto used for?

git rebase --onto is used to change the base of your current branch to another branch, effectively "moving" your branch to start from a different commit.

What is the difference between squash and fixup during interactive rebasing?

Both squash and fixup squash commits together. However, squash allows you to edit the commit message for the combined commits, while fixup discards the commit message of the squashed commit.

How do I abort a rebase if something goes wrong?

Use git rebase --abort to stop the rebase and return your branch to its original state.

I've already pushed my branch and then rebased it locally. How do I update the remote branch?

After rebasing a branch that's already been pushed, you'll need to force-push the branch with git push origin <branch-name> --force-with-lease.

Why are some people against rebasing?

Mainly because it rewrites commit history. In shared branches, this can cause confusion. It can also lead to lost work if not done carefully or if team members aren't well-coordinated.

Can I use git pull --rebase by default?

Yes! Use git config --global pull.rebase true to make git pull --rebase the default behavior for git pull.

 

Summary

Rebasing in Git is a powerful tool that allows for a cleaner, more linear commit history compared to the default merge strategy. With rebasing, you can "replay" your branch's changes onto another, ensuring your changes appear as if they happened in sequence after the other branch's changes. While it offers a clean history, rebasing can be complex, especially when misused or on shared branches, leading to potential conflicts and confusion.

To complement the git pull command, which fetches changes from a remote branch and merges them, git pull --rebase fetches those changes and rebases the current branch onto the fetched branch. It's an alternative that provides a more linear history, avoiding unnecessary merge commits.

The advanced topics like git rebase --onto and interactive rebasing with autosquash bring more flexibility and control over the commit history, offering the capability to change a branch's base or to automate the squashing process, respectively.

 

Additional Resources

  • Git Documentation: The official Git documentation provides comprehensive details about the git rebase command.
  • Pro Git Book: The Pro Git book is a valuable resource for understanding Git more deeply. The chapter on rebasing can be especially helpful.
  • Interactive Rebasing: Atlassian's tutorial on interactive rebasing is a hands-on guide to using this feature.
  • Git Branching and Merging: For a visual representation of various Git operations, including rebasing, check out this visual guide by LearnGitBranching.
  • Git Workflows: To understand where rebasing might fit into a larger Git workflow, the article "Comparing Workflows" by Atlassian is insightful.

 

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Deepak Prasad

Deepak Prasad

He is the founder of GoLinuxCloud and brings over a decade of expertise in Linux, Python, Go, Laravel, DevOps, Kubernetes, Git, Shell scripting, OpenShift, AWS, Networking, and Security. With extensive experience, he excels in various domains, from development to DevOps, Networking, and Security, ensuring robust and efficient solutions for diverse projects. You can connect with him on his LinkedIn profile.

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