post-merge hook in Git - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a post-merge hook script

Given the following post-merge hook script in a Git repository, what will be the output after a successful merge?

Git

#!/bin/sh

echo "Merge completed on $(date)"

A Merge completed on $(date)

B Merge completed on Thu Jun 1 12:00:00 UTC 2024

C Merge completed on 2024-06-01 12:00:00

D No output

💡 Hint

The date command outputs the current date and time in a default format.

The script uses command substitution $(date) which runs the date command and inserts its output. The default format of date is a full date and time string like 'Thu Jun 1 12:00:00 UTC 2024'.

🧠 Conceptual

intermediate

Purpose of the post-merge hook

What is the primary purpose of the Git post-merge hook?

A To run commands after a successful merge to update the working directory or notify users

B To reset the repository to a previous commit after merging

C To automatically commit changes before merging

D To prevent merges from happening if conflicts exist

💡 Hint

Think about what happens after a merge finishes successfully.

The post-merge hook runs after a successful merge and is typically used to update files, rebuild assets, or notify users about the merge completion.

🔀 Workflow

advanced

Correct placement of a post-merge hook script

Where should you place a custom post-merge hook script in a Git repository to ensure it runs after merges?

A root directory of the repository

B .git/post-merge

C .git/hooks/post-merge

D any directory as long as it is executable

💡 Hint

Git looks for hooks in a specific directory inside the repository.

Git expects hook scripts to be placed inside the .git/hooks directory with the exact hook name and executable permissions.

❓ Troubleshoot

advanced

Why does the post-merge hook not run?

You created a post-merge hook script in .git/hooks/ but it does not run after merges. Which is the most likely reason?

A The merge was done with --no-commit option

B The script is named post-merge.sh instead of post-merge

C The repository is not a Git repository

D The script file is not executable

💡 Hint

Git requires hook scripts to have a specific permission to run.

Git only runs hook scripts if they have executable permissions. Without it, the script is ignored.

✅ Best Practice

expert

Best practice for sharing post-merge hooks across a team

What is the best practice to share a post-merge hook script with all team members in a Git project?

A Store the hook script in the repository and use a setup script to copy it to .git/hooks/

B Commit the hook script directly inside .git/hooks/ directory

C Ask each team member to manually create the hook script locally

D Use a global Git hook directory for all repositories

💡 Hint

Git does not track files inside .git/hooks by default.

Since .git/hooks is not version controlled, the best practice is to store hook scripts in the repository (e.g., in a hooks/ folder) and provide a setup script that copies them to .git/hooks/ for each user.

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