git-workshop/01_essentials/04-merging

Module 04: Merging Branches

Learning Objectives

In this module, you will:

• Understand what merging means in Git
• Merge a feature branch back into main
• Use git merge to combine branches
• Visualize merged branches with git log --graph

Challenge

Setup

Run the setup script to create your challenge environment:

.\setup.ps1

This will create a challenge/ directory with a Git repository that has a main branch and a feature branch.

Your Task

You've been working on a new login feature in a separate branch. Now it's time to merge your work back into the main branch!

Scenario:

• You created a feature-login branch to add login functionality
• You made some commits on that branch
• Meanwhile, your teammate updated the README on main
• Now you need to bring your login feature back into main

Steps:

1. Navigate to the challenge directory: cd challenge
2. Check which branch you're on: git branch
3. View all branches: git log --oneline --graph --all
4. Merge the feature-login branch into main: git merge feature-login
5. View the result: git log --oneline --graph --all

That's it! Merging is how you bring work from one branch into another.

What is Merging?

Merging is the process of taking changes from one branch and bringing them into another branch.

Think of it like combining two streams into one river - all the water (code) flows together.

Before Merging

You have two branches with different work:

main:         A---B---C
                   \
feature-login:      D---E

• Main branch has commits A, B, and C
• Feature-login branch has commits D and E
• They split apart at commit B

After Merging

You bring the feature branch into main:

main:         A---B---C---M
                   \   /
feature-login:      D-E

• Commit M is a merge commit - it combines both branches
• Main now has all the work from both branches
• Your login feature is now part of main!

How to Merge

Merging is simple - just two steps:

1. Switch to the branch you want to merge INTO

git switch main

This is the branch that will receive the changes.

2. Merge the other branch

git merge feature-login

This brings changes from feature-login into main.

That's it! Git does the work of combining the changes.

Understanding the Merge Commit

When you merge, Git creates a special commit called a merge commit.

What makes it special?

• It has TWO parent commits (one from each branch)
• It represents the point where branches came back together
• Git writes a message like "Merge branch 'feature-login'"

You can view the merge commit just like any other commit:

git show HEAD

Visualizing Merges

Use git log --graph to see how branches merged:

git log --oneline --graph --all

Example output:

*   a1b2c3d (HEAD -> main) Merge branch 'feature-login'
|\
| * e5f6g7h (feature-login) Implement login validation
| * h8i9j0k Add login form
* | k1l2m3n Update README with setup instructions
|/
* n4o5p6q Initial project structure

Reading the graph:

• * = A commit
• | = Branch line
• / and \ = Branches splitting or joining
• (HEAD -> main) = You are here

The graph shows how the branches split and came back together!

Useful Commands

# Merging
git merge <branch-name>         # Merge a branch into current branch

# Viewing
git log --oneline --graph       # See branch history visually
git log --oneline --graph --all # Include all branches

# Branch management
git branch                      # List branches
git switch <branch-name>        # Switch to a branch
git branch -d <branch-name>     # Delete a branch (after merging)

Common Questions

"What if I'm on the wrong branch when I merge?"

Don't worry! The branch you're currently on is the one that receives the changes.

Example:

git switch main              # Go to main
git merge feature-login      # Bring feature-login INTO main

Always switch to the destination branch first!

"Can I undo a merge?"

Yes! Before you push to a remote:

git reset --hard HEAD~1

This removes the merge commit. (We'll cover this more in later modules)

"What happens to the feature branch after merging?"

The feature branch still exists! The merge just copies its commits into main.

You can delete it if you're done:

git branch -d feature-login    # Safe delete (only if merged)

The commits are still in history - you're just removing the branch label.

"What if Git can't merge automatically?"

Sometimes Git needs your help when the same lines were changed in both branches. This is called a merge conflict.

Don't worry - we'll learn how to handle conflicts in the next module!

If you encounter a conflict now and want to cancel:

git merge --abort

Verification

Once you've merged the feature-login branch, verify your solution:

.\verify.ps1

The verification script will check that you've successfully merged.

Need to Start Over?

If you want to reset the challenge and start fresh:

.\reset.ps1

What's Next?

Next module: Merge Conflicts - Learn what to do when Git can't automatically merge changes.

Later: In the advanced modules, you'll learn about different merging strategies and when to use them. For now, understanding basic merging is all you need!

Quick Summary

✅ Merging combines work from one branch into another ✅ Switch to the destination branch, then run git merge <source-branch> ✅ Git creates a merge commit to record the merge ✅ Use git log --graph to visualize how branches merged ✅ The feature branch still exists after merging - you can delete it if you want

That's all there is to basic merging! 🎉