Merge conflicts why they happen in Git - Commands & Configuration

Introduction

Merge conflicts happen when two people change the same part of a file in different ways. Git cannot decide which change to keep automatically, so it asks you to fix it.

When two developers edit the same line in a file and try to merge their changes.

When you update your branch but someone else changed the same code in the main branch.

When you rebase your work on top of new commits that touch the same files.

When merging feature branches that have overlapping changes.

When pulling changes from a remote repository that conflict with your local edits.

Commands

This command tries to merge the 'feature-branch' into your current branch. If both branches changed the same lines, Git will stop and show a conflict.

Terminal

git merge feature-branch

Expected Output

Auto-merging example.txt

CONFLICT (content): Merge conflict in example.txt

Automatic merge failed; fix conflicts and then commit the result.

Shows which files have conflicts and need your attention before you can finish the merge.

Terminal

git status

Expected Output

On branch main

You have unmerged paths.

  (fix conflicts and run "git commit")



Unmerged paths:

  (use "git add <file>..." to mark resolution)



	both modified:   example.txt



no changes added to commit (use "git add" and/or "git commit -a")

Shows the conflicting parts in the files so you can see what changed on each side.

Terminal

git diff

Expected Output

<<<<<<< HEAD

Current branch changes

=======

Feature branch changes

>>>>>>> feature-branch

Marks the conflict in 'example.txt' as resolved after you fix it manually.

Terminal

git add example.txt

Expected Output

No output (command runs silently)

Completes the merge by committing the resolved changes.

Terminal

git commit -m "Resolve merge conflict in example.txt"

Expected Output

[main 1a2b3c4] Resolve merge conflict in example.txt

Key Concept

If you remember nothing else from this pattern, remember: merge conflicts happen when Git cannot automatically decide which change to keep because the same lines were changed differently.

Common Mistakes

Ignoring the conflict markers and committing the file as is.

This leaves conflict markers in the code, causing errors and broken code.

Manually edit the file to choose or combine changes, remove conflict markers, then add and commit.

Not running 'git add' after fixing conflicts before committing.

Git will not know the conflicts are resolved and will prevent the commit.

After fixing conflicts, run 'git add <file>' to mark them resolved before committing.

Trying to merge without pulling the latest changes first.

You may get unexpected conflicts or outdated code.

Always pull or fetch and rebase to update your branch before merging.

Summary

Run 'git merge' to combine branches; conflicts happen if the same lines differ.

Use 'git status' and 'git diff' to find and understand conflicts.

Manually fix conflicts, then 'git add' and 'git commit' to complete the merge.

Practice

1. Why do merge conflicts happen in Git?

easy

A. Because Git lost the commit history

B. Because the same part of a file was changed differently in two branches

C. Because the repository is too large

D. Because the branch names are the same

Solution

1. Step 1: Understand what causes merge conflicts

   Merge conflicts happen when Git tries to combine changes but finds different edits in the same part of a file from two branches.

2. Step 2: Identify the correct cause

   Only when the same lines are changed differently does Git stop and ask for help, causing a conflict.

3. Final Answer:

   Because the same part of a file was changed differently in two branches -> Option B

4. Quick Check:

   Same file part changed differently = merge conflict [OK]

Hint: Conflicts happen when edits overlap in the same file area [OK]

Common Mistakes:

• Thinking conflicts happen due to repo size
• Believing branch names cause conflicts
• Assuming commit history loss causes conflicts

2. Which Git command is used to start a merge that might cause conflicts?

easy

A. git push

B. git branch

C. git clone

D. git merge

Solution

1. Step 1: Identify the command that combines branches

   The git merge command is used to combine changes from one branch into another.

2. Step 2: Understand when conflicts occur

   Conflicts can happen during this merge if changes overlap, so git merge is the command that triggers this process.

3. Final Answer:

   git merge -> Option D

4. Quick Check:

   git merge starts merges that may conflict [OK]

Hint: Use git merge to combine branches and check for conflicts [OK]

Common Mistakes:

• Confusing git branch with git merge
• Using git clone to merge
• Thinking git push merges branches

3. Given two branches, master and feature, both changed the same line in app.txt. What will happen when you run git merge feature on master?

medium

A. Git will automatically merge without any issues

B. Git will delete app.txt

C. Git will create a merge conflict in app.txt

D. Git will ignore changes from feature branch

Solution

1. Step 1: Analyze the changes in both branches

   Both branches changed the same line in app.txt, so Git cannot decide which change to keep automatically.

2. Step 2: Understand Git's behavior on conflicting changes

   Git will stop the merge and mark app.txt as conflicted, requiring manual resolution.

3. Final Answer:

   Git will create a merge conflict in app.txt -> Option C

4. Quick Check:

   Same line changed differently = conflict created [OK]

Hint: Same line changed in both branches causes conflict [OK]

Common Mistakes:

• Assuming Git merges automatically always
• Thinking Git deletes files on conflict
• Believing Git ignores conflicting changes

4. You ran git merge feature and got a conflict. Which step should you take to fix it?

medium

A. Edit the file to choose which changes to keep, then commit

B. Rename the branch and try merging again

C. Run git push immediately

D. Delete the conflicting file and commit

Solution

1. Step 1: Understand how to resolve merge conflicts

   When a conflict occurs, you must open the conflicting file and decide which changes to keep or combine.

2. Step 2: Complete the merge after resolving conflicts

   After editing and saving the file, you add it and commit to finish the merge process.

3. Final Answer:

   Edit the file to choose which changes to keep, then commit -> Option A

4. Quick Check:

   Resolve conflicts by editing files, then commit [OK]

Hint: Fix conflicts by editing files before committing [OK]

Common Mistakes:

• Deleting files instead of resolving conflicts
• Pushing before resolving conflicts
• Renaming branches to fix conflicts

5. Two developers edited different parts of the same file in separate branches. When merging, why might Git NOT report a conflict?

hard

A. Because changes are in different lines and Git can merge automatically

B. Because Git ignores changes in one branch

C. Because the file was deleted in one branch

D. Because the branches have the same name

Solution

1. Step 1: Understand Git's merge behavior with non-overlapping changes

   If changes are made in different parts of a file, Git can combine them automatically without conflicts.

2. Step 2: Recognize why no conflict occurs

   Since the edits do not overlap, Git merges both changes smoothly.

3. Final Answer:

   Because changes are in different lines and Git can merge automatically -> Option A

4. Quick Check:

   Non-overlapping changes merge without conflict [OK]

Hint: Different lines changed merge automatically [OK]

Common Mistakes:

• Thinking Git ignores one branch's changes
• Assuming file deletion causes no conflict
• Believing branch names affect conflicts