Branching, Merging & Conflict Resolution

Why Branches?

Branches let you develop features in isolation without affecting stable code. The main branch stays clean while you experiment on feature branches.

Branch Commands

# Create a branch
git branch feature-auth
 
# Switch to it
git switch feature-auth
# or (legacy): git checkout feature-auth
 
# Create and switch in one command
git switch -c feature-auth
 
# List branches (* = current)
git branch
 
# Delete a branch (after merging)
git branch -d feature-auth

Merging

When your feature is ready, merge it into main:

# Switch to main
git switch main
 
# Merge feature branch
git merge feature-auth
 
# Delete the merged branch
git branch -d feature-auth

Resolving Conflicts

Conflicts occur when two branches modify the same lines:

git merge feature-branch
# Auto-merging file.txt
# CONFLICT (content): Merge conflict in file.txt

The file will contain conflict markers:

<<<<<<< HEAD
Content from current branch
=======
Content from incoming branch
>>>>>>> feature-branch

Resolution:

Open the file and choose which content to keep
Remove the conflict markers (<<<<<<<, =======, >>>>>>>)
Stage and commit:

git add file.txt
git commit -m "Resolve merge conflict in file.txt"

Comparing Changes

# Differences in working directory
git diff
 
# Between branches
git diff main feature-auth
 
# Between commits
git diff abc123 def456

Viewing File History

# Who changed each line
git blame filename.txt
 
# History of a specific file
git log --follow filename.txt

Undoing Changes

Revert (Safe — creates new commit)

git revert HEAD        # Undo last commit
git revert abc123      # Undo specific commit

Reset (Destructive — removes commits)

git reset --soft HEAD~1   # Undo commit, keep changes staged
git reset --hard HEAD~1   # Undo commit AND discard changes

⚠️

git reset --hard permanently deletes changes. Never use it on commits already pushed to a shared repository.

Summary

Branches isolate work; git switch -c name creates and switches
git merge combines branches; conflicts require manual resolution
git revert safely undoes commits; git reset rewrites history
git diff shows changes; git blame shows line-by-line authorship
Tags mark releases: git tag v1.0.0

Next Steps

Next, we'll connect to GitHub — clone repos, push/pull, and collaborate with pull requests.

Learning Objectives