Chapter 3: Branch, Merge, Rebase, Stash and Pull Requests

3.7 A conflict, line by line

By Ravindra Bagale · Last updated: 25 October 2026

Why: the problem

A conflict happens when two branches change the same line of the same file, and Git cannot know which version is right. It is not an error and nothing is lost. Git stops the merge, writes both versions into the file between marker lines, and waits for you. Freshers panic, delete one side by mistake, or commit the file with the markers still inside, which breaks the build for everyone. At a company like Paytm, a broken config line can stop payments. In this lesson you will create a real conflict in badge.py of hello-shop, read the file line by line, understand the three marker lines, fix it by hand, by choosing one side, and with a merge tool, and make sure no marker is left before you commit.

What we will build

You will set BADGE_COLOR to gold on a branch and to blue on main, merge, read the conflict, keep gold, check for leftover markers, and commit. Then you will try ours/theirs, abort, and a quick tool check.

What: every term in plain English

• Conflict — Two sides changed the same lines; Git needs you to choose.
• Start marker — A line of seven less-than signs followed by HEAD. Your current branch side starts here.
• Middle marker — A line of seven equals signs (=======). It separates the two sides.
• End marker — A line of seven greater-than signs followed by the branch name. The incoming side ends here.
• Unmerged path — A file still in conflict; shown as "both modified".
• ours / theirs — In a merge, ours is the current branch; theirs is the branch you merge in.
• git merge --abort — Stop the merge and go back to before it.
• Resolve — Edit the file to the final content, remove markers, git add.

How: step by step

1. Base file

   cd ~/devops-lab/hello-shop && git switch -q main && echo 'BADGE_COLOR = "green"' > badge.py && git add . && git commit -qm "Add badge"
   

   What it does: Common start.

   Output

   (no output)
   

2. Branch says gold

   git switch -qc feature/badge-colour && sed -i 's/green/gold/' badge.py && git commit -qam "Gold badge"
   

   What it does: Change one line.

   Output

   (no output)
   

3. Main says blue

   git switch -q main && sed -i 's/green/blue/' badge.py && git commit -qam "Set campaign colour to blue"
   

   What it does: Same line, other value.

   Output

   (no output)
   

4. Merge

   git merge feature/badge-colour
   

   What it does: Git stops.

   Output

   Auto-merging badge.py
   CONFLICT (content): Merge conflict in badge.py
   Automatic merge failed; fix conflicts and then commit the result.
   

5. See status

   git status -s
   

   What it does: UU = both modified.

   Output

   UU badge.py
   

6. Count marker lines

   grep -c -E "^(=======|>>>>>>>)" badge.py
   

   What it does: Middle and end markers are in the file.

   Output

   2
   

7. Read both sides

   git show :2:badge.py; git show :3:badge.py
   

   What it does: Stage 2 is ours, stage 3 is theirs.

   Output

   BADGE_COLOR = "blue"
   BADGE_COLOR = "gold"
   

Example 1: Fix the conflict by hand and commit

Stack. Git, Python

Goal. Fix the conflict by hand and commit.

fix.sh

cat -n badge.py
printf 'BADGE_COLOR = "gold"\n' > badge.py
grep -n -E "^(=======|>>>>>>>)" badge.py || echo "no markers left"
python3 -m py_compile badge.py && echo compile-ok
git add badge.py
git commit --no-edit
git log --oneline --graph -4

What each line does

• cat -n — Five lines: start marker, blue, middle marker, gold, end marker.
• printf ... > badge.py — Write the final content: keep gold.
• grep markers — Must find nothing.
• py_compile — The file is valid Python again.
• git add — Mark as resolved.
• commit --no-edit — Finish the merge.

Green output

     2  BADGE_COLOR = "blue"
     3  =======
     4  BADGE_COLOR = "gold"
     5  >>>>>>> feature/badge-colour
no markers left
compile-ok
[main 4d4d4d4] Merge branch 'feature/badge-colour'
*   4d4d4d4 Merge branch 'feature/badge-colour'
|\
| * 2b2b2b2 Gold badge
* | 3c3c3c3 Set campaign colour to blue

Expected result. The merge is done with the colour you chose and no markers left.

Example 2: Choose a whole side fast with ours or theirs

Stack. Git

Goal. Choose a whole side fast with ours or theirs.

side.sh

git reset -q --hard HEAD~1
git merge feature/badge-colour
git checkout --theirs badge.py
cat badge.py
git add badge.py && git commit -q --no-edit
git log -1 --oneline

What each line does

• reset --hard HEAD~1 — Lab only: undo the merge to try again.
• --theirs — Take the incoming branch version (gold).
• --ours — Would keep main (blue).

Green output

CONFLICT (content): Merge conflict in badge.py
BADGE_COLOR = "gold"
5e5e5e5 Merge branch 'feature/badge-colour'

Expected result. Good for generated files like lock files where one side is clearly right.

Example 3: Abort when you are not sure

Stack. Git

Goal. Abort when you are not sure.

abort.sh

git reset -q --hard HEAD~1
git merge feature/badge-colour
git merge --abort
git status -s
cat badge.py

What each line does

• merge --abort — Go back to before the merge.
• status empty — Nothing half-done.

Green output

CONFLICT (content): Merge conflict in badge.py
BADGE_COLOR = "blue"

Expected result. You can always stop, ask the teammate, and try again later.

Example 4: Block commits that still contain markers

Stack. Git hooks

Goal. Block commits that still contain markers.

.git/hooks/pre-commit

#!/bin/sh
if git diff --cached | grep -q -E "^[+](=======|>>>>>>>)( |$)"; then
  echo "ERROR: conflict markers found. Fix them before commit."
  exit 1
fi

setup

chmod 755 .git/hooks/pre-commit
printf '=======\n' >> badge.py && git add badge.py
git commit -m "bad"
git checkout -- badge.py; git reset -q badge.py

What each line does

• git diff --cached — What you are about to commit.
• grep marker lines — Middle or end marker added.
• exit 1 — Stop the commit.
• chmod 755 — Make the hook run.

Green output

ERROR: conflict markers found. Fix them before commit.

Expected result. A small hook stops the most common conflict mistake. git diff --check also warns about markers.

Verify: did it work?

1. No unmerged files

   git diff --name-only --diff-filter=U
   

   What it does: Empty.

   Output

   (no output)
   

2. Final value

   cat badge.py
   

   What it does: The colour you chose.

   Output

   BADGE_COLOR = "gold"
   

3. Merge commit exists

   git log --merges --oneline -1
   

   What it does: Done.

   Output

   5e5e5e5 Merge branch 'feature/badge-colour'
   

When it is red 1

CONFLICT (content): Merge conflict in badge.py

Cause. Same line changed on both sides.

Fix, step by step

1. Open the file, pick the final lines, remove markers.
2. git add badge.py
3. git commit

When it is red 2

error: Committing is not possible because you have unmerged files.

Cause. You did not git add the fixed file.

Fix, step by step

1. git add FILE
2. git commit

When it is red 3

SyntaxError: invalid syntax (badge.py, line 3)

Cause. Markers were committed into the code.

Fix, step by step

1. Remove the marker lines.
2. Commit the fix.
3. Add the pre-commit hook.

When it is red 4

fatal: You have not concluded your merge (MERGE_HEAD exists).

Cause. A merge is still in progress.

Fix, step by step

1. Finish with git commit or stop with git merge --abort.

Cleanup

1. Delete branch

   git branch -d feature/badge-colour
   

   What it does: Merged now.

   Output

   Deleted branch feature/badge-colour (was 2b2b2b2).
   

Practice tasks

Homework: try at home

Recap

• A conflict is a question, not a failure.
• HEAD side, middle marker, incoming side.
• Edit, remove markers, git add, commit.
• --abort to start over.
• Check for markers before commit.

FAQ

Can Git lose my code in a conflict?

No. Both sides are in the file and in stages 2 and 3.

What is zdiff3?

A style that also shows the base version, which helps you see what each side changed.

Can VS Code help?

Yes, it shows Accept Current, Accept Incoming and Accept Both buttons.

Why do lock files conflict often?

Many people change them; regenerate them instead of editing by hand.

How do I avoid conflicts?

Small branches, merge often, and pull main daily.

Interview questions

1. How do you resolve a merge conflict?

   Open the files, choose the final content, remove markers, test, git add, commit.

2. What are ours and theirs?

   In a merge, ours is the current branch and theirs is the incoming branch.

3. How do you cancel a merge?

   git merge --abort.

4. How do you list conflicted files?

   git diff --name-only --diff-filter=U.

5. How do you reduce conflicts in a team?

   Short-lived branches, frequent merges from main, clear code ownership.

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