post-merge hook in Git - Mini Project: Build & Apply

Using a Git post-merge Hook to Automate Tasks

📖 Scenario: You work on a team project using Git. After merging changes from others, you want to automatically run a script that updates dependencies to keep your project ready to use.

🎯 Goal: Create a Git post-merge hook script that runs npm install automatically after every merge.

📋 What You'll Learn

Create a post-merge hook file in the .git/hooks directory

Make the post-merge hook executable

Write a script inside the hook that runs npm install

Test the hook by performing a merge and observing the output

💡 Why This Matters

🌍 Real World

Automating tasks after Git merges saves time and reduces errors by running commands like dependency installs or tests automatically.

💼 Career

Many DevOps and developer roles require knowledge of Git hooks to automate workflows and improve team productivity.

1

Create the post-merge hook file

Create a file named post-merge inside the .git/hooks directory.

Git

# Create the file .git/hooks/post-merge
# Your code here

Hint

Use the touch command in your terminal to create the file.

2

Make the post-merge hook executable

Make the .git/hooks/post-merge file executable by running chmod +x .git/hooks/post-merge.

Git

# Create the file .git/hooks/post-merge
# Make the file executable
# Your code here

Hint

Use chmod +x to allow the script to run.

3

Write the script to run npm install

Edit the .git/hooks/post-merge file to add the line npm install so it runs automatically after a merge.

Git

# Create the file .git/hooks/post-merge
# Make the file executable
chmod +x .git/hooks/post-merge

# Add the command to run npm install
# Your code here

Hint

Start the script with #!/bin/sh and then add npm install on the next line.

4

Test the post-merge hook

Perform a Git merge and observe that npm install runs automatically by checking the output in your terminal.

Git

# Create the file .git/hooks/post-merge
# Make the file executable
chmod +x .git/hooks/post-merge

#!/bin/sh
npm install

# Now perform a git merge in your terminal to test
# Your code here

Hint

After merging, you should see npm installing packages automatically.

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