post-merge hook in Git - Step-by-Step Execution

Process Flow - post-merge hook

Merge completes

↓

Git detects post-merge hook script

↓

Execute post-merge hook script

↓

Script runs commands (e.g., build, tests)

↓

Hook finishes

↓

Merge process ends

After a git merge finishes, Git runs the post-merge hook script if it exists, allowing automated tasks like rebuilding or testing.

Execution Sample

Git

#!/bin/sh
# post-merge hook example
echo "Merge completed"
make build
git status

This post-merge hook prints a message, runs a build, and shows git status after a merge.

Process Table

Step	Action	Command Run	Output	Result
1	Merge finishes	git merge branch	Merge successful	Merge completed
2	Detect post-merge hook	Check .git/hooks/post-merge	Script found	Prepare to run script
3	Run post-merge hook	echo "Merge completed"	Merge completed	Message shown
4	Run build command	make build	Build successful	Project rebuilt
5	Show git status	git status	On branch main nothing to commit	Status displayed
6	Hook ends	Script exits	No errors	Merge process complete

💡 Post-merge hook script finishes after running commands, merge process ends.

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	Final
Merge Status	Not merged	Merged	Merged	Merged	Merged
Hook Script Found	No	Yes	Yes	Yes	Yes
Build Status	Not built	Not built	Built	Built	Built
Git Status Output	N/A	N/A	N/A	On branch main nothing to commit	On branch main nothing to commit

Key Moments - 3 Insights

Why does the post-merge hook run only after the merge finishes?

Because the post-merge hook is triggered by Git only after the merge completes successfully, as shown in execution_table step 1 and 2.

What happens if the post-merge hook script is missing or not executable?

Git skips running the hook, so no commands run after merge; this is implied by step 2 where script detection is required.

Can the post-merge hook affect the merge result?

No, the hook runs after merge completes; it can run commands but cannot change the merge outcome, as seen in step 6.

Visual Quiz - 3 Questions

Look at the execution table, what command runs at step 4?

A git status

B echo "Merge completed"

C make build

D git merge branch

💡 Hint

Check the 'Command Run' column at step 4 in the execution_table.

At which step does Git detect the post-merge hook script?

A Step 2

B Step 3

C Step 1

D Step 5

💡 Hint

Look for 'Detect post-merge hook' action in the execution_table.

If the build command fails at step 4, what would change in the execution flow?

A The hook script would continue to step 5 normally

B The hook script would stop and not run git status

C Git would abort the merge

D The merge would be undone automatically

💡 Hint

Consider that post-merge hook runs commands sequentially; failure usually stops the script.

Concept Snapshot

post-merge hook:
- Runs automatically after a successful git merge
- Located in .git/hooks/post-merge
- Can run scripts like build, tests, or notifications
- Does not affect merge success
- Useful for automating post-merge tasks

Full Transcript

The post-merge hook is a script Git runs automatically after a merge finishes successfully. It is located in the .git/hooks directory and named post-merge. When a merge completes, Git checks if this script exists and is executable. If yes, Git runs it. The script can perform tasks like rebuilding the project, running tests, or showing status. The hook runs after the merge, so it cannot change the merge result. If the script is missing or fails, Git continues but the post-merge tasks may not complete. This hook helps automate steps you want to happen right after merging code.

Practice

1. What is the main purpose of the post-merge hook in Git?

easy

A. To create a new branch after merging

B. To prevent merges from happening

C. To delete merged branches automatically

D. To run commands automatically after a merge completes

Solution

1. Step 1: Understand the role of Git hooks

   Git hooks are scripts that run at specific points in Git workflows to automate tasks.

2. Step 2: Identify the specific timing of the post-merge hook

   The post-merge hook runs right after a merge finishes, allowing automation of follow-up tasks.

3. Final Answer:

   To run commands automatically after a merge completes -> Option D

4. Quick Check:

   post-merge hook = runs after merge [OK]

Hint: Post-merge hook runs after merge finishes [OK]

Common Mistakes:

• Confusing post-merge with pre-merge hooks
• Thinking it prevents merges
• Assuming it creates or deletes branches

2. Which of the following is the correct way to make a post-merge hook script executable on a Unix-like system?

easy

A. chmod 777 .git/hooks/post-merge

B. chmod +x .git/hooks/post-merge

C. git hook enable post-merge

D. chmod 644 .git/hooks/post-merge

Solution

1. Step 1: Understand file permissions for executable scripts

   To run a script as a hook, it must have executable permission, usually set with chmod +x.

2. Step 2: Identify the correct command

   chmod +x .git/hooks/post-merge sets the executable bit without giving excessive permissions.

3. Final Answer:

   chmod +x .git/hooks/post-merge -> Option B

4. Quick Check:

   Make hook executable = chmod +x [OK]

Hint: Use chmod +x to make hook executable [OK]

Common Mistakes:

• Using chmod 777 which is insecure
• Using chmod 644 which is not executable
• Trying git commands to enable hooks

3. Given this post-merge hook script saved in .git/hooks/post-merge and made executable:

#!/bin/sh
npm install
npm run build

What will happen after you run git merge feature-branch?

medium

A. The dependencies will install and the project will build automatically

B. The merge will fail because of the script

C. Nothing happens because post-merge hooks do not run automatically

D. Only npm install will run, not npm run build

Solution

1. Step 1: Understand what the post-merge hook script does

   The script runs npm install to install dependencies, then npm run build to build the project.

2. Step 2: Know when the post-merge hook runs

   It runs automatically after a successful merge, so both commands will execute in order.

3. Final Answer:

   The dependencies will install and the project will build automatically -> Option A

4. Quick Check:

   post-merge runs script after merge [OK]

Hint: Post-merge runs script commands after merge [OK]

Common Mistakes:

• Thinking hooks don't run automatically
• Assuming only first command runs
• Believing merge fails due to hook

4. You wrote a post-merge hook script but it does not run after merging. Which of these is the most likely cause?

medium

A. The script file is not executable

B. You forgot to commit the hook script

C. The merge was done with git rebase

D. The script is saved outside the .git/hooks directory

Solution

1. Step 1: Check script execution permissions

   If the script is not executable, Git will not run it after merge.

2. Step 2: Understand that hooks are local and not committed

   Hooks are not shared via commits, so forgetting to commit is irrelevant.

3. Step 3: Consider merge method and script location

   Rebase does not trigger post-merge, but the question states a merge was done. Also, hooks must be in .git/hooks.

4. Final Answer:

   The script file is not executable -> Option A

5. Quick Check:

   Non-executable script = hook won't run [OK]

Hint: Check if hook script has executable permission [OK]

Common Mistakes:

• Thinking hooks are shared via commits
• Confusing merge with rebase triggers
• Saving script outside .git/hooks folder

5. You want to ensure that after every merge, your Python project automatically installs new dependencies listed in requirements.txt and runs tests. Which post-merge hook script is the best choice?

hard

A. #!/bin/sh
git pull
pytest

B. #!/bin/sh
npm install
npm test

C. #!/bin/sh
pip install -r requirements.txt
pytest

D. #!/bin/sh
pip uninstall -r requirements.txt
pytest

Solution

1. Step 1: Identify the correct commands for Python dependency installation and testing

   pip install -r requirements.txt installs dependencies; pytest runs tests.

2. Step 2: Evaluate other options for relevance

   #!/bin/sh npm install npm test uses npm commands for JavaScript, not Python. #!/bin/sh pip uninstall -r requirements.txt pytest uninstalls dependencies which is wrong. #!/bin/sh git pull pytest pulls changes again, unnecessary after merge.

3. Final Answer:

   #!/bin/sh pip install -r requirements.txt pytest -> Option C

4. Quick Check:

   Python post-merge = pip install + pytest [OK]

Hint: Use pip install and pytest for Python post-merge tasks [OK]

Common Mistakes:

• Using npm commands for Python projects
• Uninstalling dependencies instead of installing
• Running git pull again after merge