Overview

Understanding the difference between rebase and merge in Git is crucial for managing branches and the project history in a clean and efficient way. Both commands are designed to integrate changes from one branch into another, but they do it in very different manners, affecting the project history and the ease of following and understanding this history.

Key Concepts

1. Branch Integration: How changes from different branches are combined.
2. Project History: The impact on the readability and linearization of project history.
3. Conflict Resolution: Handling conflicts during rebase and merge operations.

Common Interview Questions

Basic Level

1. What is the basic difference between git merge and git rebase?
2. How do you perform a basic merge of two branches?

Intermediate Level

3. Can you explain how git rebase affects the commit history compared to git merge?

Advanced Level

4. In what scenarios would you prefer rebase over merge to maintain project history?

Detailed Answers

1. What is the basic difference between git merge and git rebase?

Answer: The basic difference between git merge and git rebase lies in how they integrate changes from one branch into another and affect the project's commit history. git merge combines the histories of the merged branches, creating a new merge commit that has two parent commits. This preserves the exact history of changes but can lead to a non-linear project history. In contrast, git rebase rewrites the commit history by applying changes from one branch onto another, creating a linear sequence of commits. This can make the project history easier to read but modifies the commit history, which can be problematic in shared branches.

Key Points:
- Merge preserves the history but can lead to a non-linear, complex history graph.
- Rebase creates a linear history by reapplying commits on top of another branch.
- Merge is non-destructive, while rebase can rewrite history.

Example:

// This is a conceptual example, as Git commands are not directly applicable in C#
// Imagine merging feature_branch into master

void MergeExample()
{
    Console.WriteLine("Before merge: feature_branch and master have diverged.");
    Console.WriteLine("Running 'git merge feature_branch' on master.");
    Console.WriteLine("After merge: master contains a new merge commit combining changes.");
}

void RebaseExample()
{
    Console.WriteLine("Before rebase: feature_branch is based on an old commit of master.");
    Console.WriteLine("Running 'git rebase master' on feature_branch.");
    Console.WriteLine("After rebase: feature_branch's commits are reapplied on top of master's current state.");
}

2. How do you perform a basic merge of two branches?

Answer: To perform a basic merge of two branches, you would first check out to the branch that you want to merge the changes into, and then use the git merge command with the name of the branch you want to merge from. This will integrate the changes from the source branch into the target branch, possibly creating a merge commit if the branches have diverged.

Key Points:
- Ensure you are on the target branch before merging.
- Use git merge <branch-name> to merge changes from <branch-name> into the current branch.
- Handle any merge conflicts that arise.

Example:

void MergeBranchesExample()
{
    Console.WriteLine("Checking out to the master branch: 'git checkout master'");
    Console.WriteLine("Merging feature_branch into master: 'git merge feature_branch'");
    Console.WriteLine("If there are no conflicts, the merge is successful.");
}

3. Can you explain how git rebase affects the commit history compared to git merge?

Answer: git rebase changes the base of the current branch to be the tip of another branch, effectively moving all the work that was done on the current branch to the top of the branch history. This results in a cleaner, more linear history as opposed to git merge, which inserts a new merge commit into the history, maintaining the separate paths that divergent branches took. While rebase creates a cleaner history, it rewrites commits, which can be dangerous if the commits are shared with others.

Key Points:
- Rebase rewrites history to create a linear progression of changes.
- Merge maintains the true historical branching and merging points.
- Rebase should be used carefully, especially with public/shared branches.

Example:

void RebaseHistoryExample()
{
    Console.WriteLine("Initial: feature_branch is based on an older commit of master.");
    Console.WriteLine("Running 'git rebase master' on feature_branch.");
    Console.WriteLine("Result: feature_branch's commits are now on top of master's latest commit.");
}

4. In what scenarios would you prefer rebase over merge to maintain project history?

Answer: Rebase is preferred over merge in scenarios where a clean, linear project history is desired, such as before integrating a feature branch into the main branch. It is particularly useful for local branch management, where you want to update your feature branch with the latest changes from the main branch without creating additional merge commits. Rebase is also beneficial for preparing a series of commits before submitting them for review in a pull request, as it allows for easy commit squashing and reordering.

Key Points:
- Use rebase for updating feature branches with changes from the main branch.
- Rebase helps in cleaning up commit history before merging into shared branches.
- Avoid rebasing public/shared branches where history should be preserved.

Example:

void RebaseScenarioExample()
{
    Console.WriteLine("Feature branch development is based on an outdated commit of master.");
    Console.WriteLine("Running 'git rebase master' on the feature branch to move its changes on top of master's latest commits.");
    Console.WriteLine("This results in a cleaner, more linear history that's easier to merge into master.");
}