Client-side vs server-side hooks in Git - Hands-On Comparison

Understanding Client-side vs Server-side Git Hooks

📖 Scenario: You are working on a team project using Git for version control. Your team wants to automate checks to improve code quality and consistency. You will learn how to set up simple client-side and server-side Git hooks to automate tasks before commits and before pushing code to the shared repository.

🎯 Goal: Build a basic Git setup with a client-side pre-commit hook that checks commit messages and a server-side pre-receive hook that rejects pushes with empty commit messages.

📋 What You'll Learn

Create a client-side pre-commit hook script

Create a server-side pre-receive hook script

Understand where to place client-side and server-side hooks

Test the hooks by making commits and pushes

💡 Why This Matters

🌍 Real World

Teams use Git hooks to automate code quality checks and enforce rules before code is committed or pushed.

💼 Career

Understanding Git hooks is important for developers and DevOps engineers to maintain code standards and automate workflows.

1

Set up a client-side pre-commit hook

Create a file named pre-commit inside the .git/hooks/ directory of your local repository. Add a script that checks if the commit message is not empty by reading the commit message file .git/COMMIT_EDITMSG. The script should exit with status 1 if the message is empty, preventing the commit.

Git

# Create a client-side pre-commit hook script in .git/hooks/pre-commit
# Your code here

Hint

The pre-commit hook runs before the commit is finalized. Use shell script syntax to check if the commit message file is empty.

2

Set up a server-side pre-receive hook

Create a file named pre-receive inside the hooks/ directory of the remote bare Git repository. Add a script that reads commit messages from the pushed commits and rejects the push if any commit message is empty by exiting with status 1.

Git

# Create a server-side pre-receive hook script in hooks/pre-receive
# Your code here

Hint

The pre-receive hook runs on the server before accepting pushed commits. Use git rev-list to get commits and check their messages.

3

Make a commit to test the client-side hook

Create a commit with an empty commit message in your local repository to test that the client-side pre-commit hook prevents the commit.

Git

# Create an empty commit message to test the client-side pre-commit hook
# Your code here

Hint

Use git commit --allow-empty -m "" to create a commit with an empty message and trigger the pre-commit hook.

4

Push commits to test the server-side hook

Push your commits to the remote repository to test that the server-side pre-receive hook rejects pushes with empty commit messages. Use git push and observe the error message.

Git

# Push commits to test the server-side pre-receive hook
# Your code here

Hint

Run git push and check the output for the rejection message from the server-side hook.

Practice

1. Which of the following best describes a client-side Git hook?

easy

A. A Git command to clone repositories.

B. A script that runs on the Git server to control repository access.

C. A tool to merge branches automatically on the server.

D. A script that runs on your local machine before or after Git actions like commit or push.

Solution

1. Step 1: Understand client-side hooks context

   Client-side hooks run on your local computer and trigger before or after Git commands like commit or push.

2. Step 2: Differentiate from server-side hooks

   Server-side hooks run on the Git server to enforce rules for all users, unlike client-side hooks which are local.

3. Final Answer:

   A script that runs on your local machine before or after Git actions like commit or push. -> Option D

4. Quick Check:

   Client-side hook = local script [OK]

Hint: Client-side hooks run locally before/after Git commands [OK]

Common Mistakes:

• Confusing client-side hooks with server-side hooks
• Thinking hooks run only on the server
• Assuming hooks are Git commands

2. Which of the following is the correct location to place a client-side pre-commit hook script in a Git repository?

easy

A. /usr/local/git/hooks/pre-commit

B. .git/hooks/server-pre-commit

C. .git/hooks/pre-commit

D. .git/pre-commit

Solution

1. Step 1: Identify the standard hooks directory

   Git client-side hooks are stored inside the .git/hooks directory of the local repository.

2. Step 2: Confirm the correct hook filename

   The pre-commit hook script must be named exactly 'pre-commit' inside .git/hooks.

3. Final Answer:

   .git/hooks/pre-commit -> Option C

4. Quick Check:

   Client-side hooks live in .git/hooks [OK]

Hint: Client-side hooks go in .git/hooks folder [OK]

Common Mistakes:

• Placing hooks outside the .git directory
• Using wrong filenames for hooks
• Confusing server-side hook locations

3. Given this server-side hook script named pre-receive on the Git server:

#!/bin/sh
while read oldrev newrev refname
 do
   if [ "$refname" = "refs/heads/main" ]; then
     echo "Pushes to main branch are not allowed."
     exit 1
   fi
 done
exit 0

What will happen if a user tries to push commits to the main branch?

medium

A. The push will be rejected with the message 'Pushes to main branch are not allowed.'

B. The push will succeed without any message.

C. The push will be accepted but with a warning.

D. The server will crash due to a syntax error.

Solution

1. Step 1: Analyze the pre-receive hook logic

   The script reads each ref being pushed. If the ref is 'refs/heads/main', it prints a message and exits with status 1, which rejects the push.

2. Step 2: Understand Git hook exit codes

   Exiting with 1 means failure, so Git rejects the push and shows the message to the user.

3. Final Answer:

   The push will be rejected with the message 'Pushes to main branch are not allowed.' -> Option A

4. Quick Check:

   Exit 1 in server hook rejects push [OK]

Hint: Exit code 1 in server hook blocks push [OK]

Common Mistakes:

• Assuming push succeeds despite exit 1
• Confusing client-side and server-side hook effects
• Ignoring the printed message

4. You wrote a client-side pre-commit hook script but it does not run when you commit. What is the most likely reason?

medium

A. The script is placed in the wrong directory on the server.

B. The script file is not executable.

C. Git does not support pre-commit hooks.

D. You forgot to push the hook to the remote repository.

Solution

1. Step 1: Check script permissions

   Client-side hooks must be executable files. If not, Git will ignore them silently.

2. Step 2: Verify hook location and Git support

   The hook must be in .git/hooks locally. Git supports pre-commit hooks, and pushing hooks to remote does not affect local hooks.

3. Final Answer:

   The script file is not executable. -> Option B

4. Quick Check:

   Hooks must be executable to run [OK]

Hint: Make hook scripts executable with chmod +x [OK]

Common Mistakes:

• Placing hooks on the server for client-side use
• Thinking Git lacks pre-commit hooks
• Expecting hooks to transfer via git push

5. You want to enforce that all commits pushed to the shared repository have a signed commit message. Which hook setup is best to ensure this rule is always checked regardless of the user's local setup?

hard

A. Implement a server-side pre-receive hook that rejects unsigned commits.

B. Ask each developer to add a client-side commit-msg hook to check signatures.

C. Use a client-side pre-push hook to warn about unsigned commits.

D. Rely on GitHub or GitLab UI to manually check commit signatures.

Solution

1. Step 1: Understand enforcement scope

   Client-side hooks depend on each user's setup and can be bypassed or missing.

2. Step 2: Use server-side hooks for mandatory checks

   Server-side hooks run on the shared repository and can reject pushes that don't meet rules, ensuring enforcement for all users.

3. Final Answer:

   Implement a server-side pre-receive hook that rejects unsigned commits. -> Option A

4. Quick Check:

   Server hooks enforce rules for all pushes [OK]

Hint: Use server-side hooks to enforce rules for all users [OK]

Common Mistakes:

• Relying only on client-side hooks for enforcement
• Assuming UI checks block pushes automatically
• Ignoring that client hooks can be disabled