Git merge and Git rebase

What is the bloody difference ?

Git-rebase and Git-merge are two methods for integrating code from two different branches. It is like the inverse of a bifurcation process. It may be called ‘code sexual reproduction’. The genomes of both branches need to combine in a specific way that produces a new commit. We expect that, with continuous integration (CI/CD), these modifications result in a viable entity, that is, software that runs without problems; passed all its test.

These two methods are implemented in the git software as git merge and git rebase. We can , thus, begin to analyse the difference between both by studying their syntax.

What follows my conversation with ChatGPT:

What is the syntax of git merge ?

The syntax for the git merge command in Git is as follows:

git merge [<options>] <branch>

Here’s a breakdown of the syntax components:

  • git merge: This is the base command to perform a merge operation in Git.
  • <options>: Optional flags that modify the behaviour of the merge operation. Some commonly used options include --no-ff to disable fast-forward merging and --squash to merge changes as a single commit.
  • <branch>: The branch you want to merge into the current branch. It can be specified as a branch name, a remote branch reference (e.g., origin/branch-name), or a commit hash.

How does it work?

When you run git merge <branch>, Git attempts to combine the changes from the specified branch into the current branch. It performs a “three-way merge” by comparing the changes between the common ancestor of the two branches (the merge base) and the HEAD commit of the current branch with the latest commit of the branch you’re merging.

During the merge, Git automatically applies the changes from the other branch and creates a new merge commit if there are conflicting changes. If there are no conflicts, Git performs a “fast-forward” merge, which moves the current branch pointer to the latest commit of the other branch.

After running the git merge command, Git may prompt you to resolve any conflicts manually if it couldn’t automatically merge all changes. You can use tools like a text editor or a dedicated merge tool to resolve conflicts. Once conflicts are resolved, you need to stage the changes and create a new commit to finalize the merge.

It’s important to note that the git merge command affects the commit history, so it’s a good practice to review and understand the changes before merging branches to ensure a clean and accurate merge.

What is the role of rebase in this context?

In the context of merging in Git, the git rebase command is an alternative approach to incorporating changes from one branch into another. While git merge combines the changes from different branches, git rebase integrates the commits from one branch onto another branch as if they were made on top of the other branch.

The role of git rebase is to maintain a linear commit history by moving, or “replaying,” the commits from the source branch onto the target branch. This can make the commit history cleaner and easier to follow, especially when dealing with long-running feature branches or branches with frequent commits.

When you perform a rebase, Git identifies the common ancestor commit between the current branch and the branch you want to rebase onto. It then applies the commits from the current branch one by one on top of the target branch, effectively “replaying” the changes. This can result in a linear sequence of commits without the additional merge commits that git merge creates.

Here’s a summary of the steps involved in a typical rebase workflow:

  1. Switch to the target branch: git checkout <target-branch>
  2. Start the rebase: git rebase <source-branch>
  3. Git will identify the common ancestor commit and replay the commits from <source-branch> on top of <target-branch>.
  4. If there are conflicts, Git will pause the rebase process, allowing you to resolve the conflicts manually.
  5. After resolving conflicts, stage the changes: git add <resolved-files>
  6. Resume the rebase: git rebase --continue
  7. Repeat steps 4-6 if there are additional conflicts until the rebase is complete.
  8. Once the rebase finishes successfully, the source branch is effectively incorporated into the target branch.

It’s important to note that git rebase rewrites the commit history, so it should be used with caution, especially when collaborating with others. If the source branch has been shared with others or pushed to a remote repository, you may need to communicate and coordinate the rebase to prevent conflicts for other users.

In summary, the role of git rebase in the context of merging is to integrate commits from one branch onto another while maintaining a linear commit history. It offers an alternative to git merge for incorporating changes and can result in a cleaner commit history.

What is the difference then?

The main difference between git merge and git rebase lies in how they incorporate changes from one branch into another and the resulting commit history.

git merge:

  • Combines the changes from a source branch into a target branch.
  • Creates a new merge commit to represent the merge operation, even if it’s a fast-forward merge.
  • Preserves the individual commits from both the source and target branches in the commit history.
  • Produces a commit graph that shows the branching and merging history of the repository.
  • Is suitable for merging feature branches, hotfixes, or integrating changes from multiple developers.

git rebase:

  • Integrates the commits from a source branch onto a target branch, making it appear as if the commits were made on top of the target branch from the beginning.
  • Does not create a merge commit unless there are conflicts that need to be resolved manually.
  • Rewrites the commit history of the source branch, creating new commits with different parent commits.
  • Produces a linear commit history without additional merge commits.
  • Can result in a cleaner and more straightforward commit history but can be disruptive when used on shared or public branches.

In summary, the key differences between git merge and git rebase are:

  • git merge combines branches, creates merge commits, and preserves the commit history of both branches.
  • git rebase integrates branches, rewrites commit history, and produces a linear commit history.

The choice between using git merge or git rebase depends on the specific scenario and your preferences for the commit history. Use git merge when you want to merge branches while preserving the original commits and their context. Use git rebase when you prefer a linear commit history and want to incorporate changes from one branch onto another as if they were made on top of the target branch.

Published by

Juan Escamilla Mólgora

Hago ecología matemática y computacional para grandes datos ambientales bajo plataformas descentralizadas basadas en la nube. En particular estoy investigando métodos novedosos de fusión de datos mutirelacionados para mejorar los modelos de predicción de especies biológicas. También diseñé y programé el Sistema de Alerta temprana de Incendios para México y Centro América

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