Difference between `git merge` and `git rebase`

git merge and git rebase are both Git commands used for combining changes from different branches. However, they do so in different ways, and each has its advantages and use cases. Let’s delve into the technical details of each:

git merge

Description

git merge integrates changes from one branch into another. It creates a new commit that combines the changes from the source branch into the target branch. This creates a merge commit that has two parent commits, representing the history of both branches.

Example

Let’s assume the following commit history:

Now, we want to merge feature-branch into main using git merge. After the merge, a new merge commit (M) is created:

# Switch to the target branch
git checkout main

# Perform the merge
git merge feature-branch

Resulting in:

Here, the commit history explicitly shows the merge commit (M) that brings in changes from feature-branch into main.

git rebase

Description

git rebase is used to combine changes from one branch into another by applying each commit in the source branch on top of the target branch. This effectively rewrites the commit history of the source branch, creating a linear history without merge commits.

Example

Assuming the same initial commit history and the same branches, feature-branch and main:

Now, we want to rebase feature-branch onto main using git rebase:

# Switch to the source branch
git checkout feature-branch

# Perform the rebase
git rebase main

Resulting in a linear history without merge commits:

Here, each commit in feature-branch has been applied on top of the latest commit in main, resulting in a linear history without a merge commit.

Differences

1. Commit History:

   • git merge preserves the commit history of both branches by creating a new merge commit.
   • git rebase creates a linear commit history by applying the changes of the source branch on top of the target branch.

2. Merge Commits:

   • git merge introduces merge commits, which explicitly show when branches were merged.
   • git rebase avoids merge commits, resulting in a cleaner, linear history.

3. Branch Visibility:

   • git merge keeps the branch structure more visible in the commit history.
   • git rebase can make it appear as if changes in the source branch occurred directly on top of the target branch.

4. Conflict Resolution:

   • In both cases, conflicts may arise when combining changes. However, conflict resolution is typically easier with git merge as Git automatically handles most conflicts.

Use Cases

• Use git merge when you want to preserve the history of both branches and want explicit merge commits.

• Use git rebase when you want a clean, linear history and are willing to rewrite the commit history of the source branch.

Note: It’s important to be cautious with rebasing, especially on shared branches, as it rewrites commit history and can cause conflicts for collaborators. Use it primarily for local branches or feature branches that haven’t been shared with others.