Creating custom hook scripts in Git - Practice Exercises

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a pre-commit hook script

You have a pre-commit hook script that checks for TODO comments in staged files. What will be the output if a staged file contains a TODO comment?

Git

#!/bin/sh
if git diff --cached | grep -q 'TODO'; then
  echo "Commit blocked: TODO comments found."
  exit 1
fi
exit 0

A Commit successful with TODO comments.

B Syntax error in hook script.

C No output, commit proceeds.

D Commit blocked: TODO comments found.

💡 Hint

The script blocks commits if TODO comments are detected in staged changes.

The script searches staged changes for 'TODO'. If found, it prints a message and exits with status 1, blocking the commit.

🧠 Conceptual

intermediate

Purpose of Git hook scripts

What is the primary purpose of creating custom Git hook scripts?

A To automate tasks during Git events like commit or push.

B To change the Git repository URL.

C To increase the size of the Git repository.

D To create new branches automatically.

💡 Hint

Think about what happens automatically when you commit or push.

Git hooks run scripts automatically on certain Git events to automate checks or tasks.

❓ Configuration

advanced

Correct placement of a custom Git hook script

Where should you place a custom hook script named 'pre-push' to ensure Git runs it before pushing?

A .git/hooks/pre-push

B .git/pre-push

C hooks/pre-push

D pre-push/.git/hooks

💡 Hint

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

Git hook scripts must be placed inside the .git/hooks directory with the exact hook name.

❓ Troubleshoot

advanced

Why a Git hook script is not running

You created a 'post-commit' hook script but it does not run after commits. What is the most likely reason?

A Git does not support post-commit hooks.

B The script is placed in the wrong directory.

C The script file is not executable.

D The repository is not initialized.

💡 Hint

Git requires hook scripts to have execute permissions.

If the hook script is not executable, Git will ignore it and not run it.

🔀 Workflow

expert

Sequence of Git hook scripts during a commit

What is the correct order of Git hook scripts triggered during a commit?

A 1,2,3,4

B 2,1,3,4

C 2,3,1,4

D 1,3,2,4

💡 Hint

Some hooks run before the commit message is prepared.

The order is: prepare-commit-msg, pre-commit, commit-msg, then post-commit.

Practice

1. What is the main purpose of creating a custom Git hook script?

easy

A. To delete branches remotely

B. To change the Git commit message manually

C. To create new Git repositories

D. To run scripts automatically at specific Git events

Solution

1. Step 1: Understand Git hooks

   Git hooks are scripts that run automatically at certain points in Git's workflow, like before a commit or after a push.

2. Step 2: Identify the purpose of custom hooks

   Custom hooks let you automate tasks or enforce rules during these Git events without manual intervention.

3. Final Answer:

   To run scripts automatically at specific Git events -> Option D

4. Quick Check:

   Git hooks = automatic scripts at Git events [OK]

Hint: Hooks run scripts automatically at Git events [OK]

Common Mistakes:

• Thinking hooks manually change commit messages
• Confusing hooks with branch deletion
• Assuming hooks create repositories

2. Which of the following is the correct way to make a Git hook script executable on Linux or macOS?

easy

A. chmod +x .git/hooks/pre-commit

B. git hook enable pre-commit

C. chmod 777 .git/hooks/pre-commit

D. git config hook.pre-commit true

Solution

1. Step 1: Understand file permissions for hooks

   Git hooks must be executable files to run automatically.

2. Step 2: Use the correct command to make a file executable

   The command chmod +x adds execute permission without changing other permissions.

3. Final Answer:

   chmod +x .git/hooks/pre-commit -> Option A

4. Quick Check:

   Make hook executable = chmod +x [OK]

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

Common Mistakes:

• Using git commands that don't exist for hooks
• Setting overly permissive permissions like 777
• Trying to enable hooks via git config

3. Given this pre-commit hook script placed in .git/hooks/pre-commit and made executable:

#!/bin/sh
if git diff --cached --quiet; then
  echo "No changes staged for commit."
  exit 1
fi

What happens when you try to commit without staging any changes?

medium

A. The commit is blocked with message 'No changes staged for commit.'

B. The commit proceeds normally without any message

C. The commit is blocked with a syntax error

D. The commit proceeds but shows a warning

Solution

1. Step 1: Analyze the script logic

   The script checks if there are no staged changes using git diff --cached --quiet. If true, it prints a message and exits with code 1.

2. Step 2: Understand Git hook exit codes

   Exiting with code 1 in a pre-commit hook stops the commit process and shows the message.

3. Final Answer:

   The commit is blocked with message 'No changes staged for commit.' -> Option A

4. Quick Check:

   Exit 1 in pre-commit = block commit [OK]

Hint: Exit non-zero in pre-commit stops commit [OK]

Common Mistakes:

• Assuming commit proceeds despite exit 1
• Confusing staged vs unstaged changes
• Expecting syntax errors from correct shell script

4. You wrote this post-commit hook script but it does not run after commits:

#!/bin/sh
echo "Commit done!"

Which is the most likely reason?

medium

A. The script filename is incorrect

B. The script is not executable

C. Git hooks cannot echo messages

D. The script must be in the project root, not .git/hooks

Solution

1. Step 1: Check common hook issues

   Hooks must be executable files inside .git/hooks/ with correct names.

2. Step 2: Identify the most common cause

   Often, scripts don't run because they lack execute permission, even if named correctly.

3. Final Answer:

   The script 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 scripts outside .git/hooks directory
• Assuming echo is not allowed in hooks
• Using wrong hook filenames

5. You want to create a custom Git hook that prevents commits if the commit message does not contain the word 'JIRA'. Which script placed in .git/hooks/commit-msg will achieve this?

hard

A. #!/bin/sh
if grep -q 'JIRA' "$1"; then
exit 1
fi

B. #!/bin/sh
grep 'JIRA' "$1" || echo "Commit message missing JIRA"

C. #!/bin/sh
if ! grep -q 'JIRA' "$1"; then
echo "Commit message must include 'JIRA'."
exit 1
fi

D. #!/bin/sh
echo "Checking commit message for JIRA"

Solution

1. Step 1: Understand commit-msg hook argument

   The commit message file path is passed as the first argument ($1) to the script.

2. Step 2: Check script logic for enforcing 'JIRA'

   #!/bin/sh if ! grep -q 'JIRA' "$1"; then echo "Commit message must include 'JIRA'." exit 1 fi uses grep -q to check if 'JIRA' is missing, then prints a message and exits with 1 to block the commit.

3. Step 3: Evaluate other options

   #!/bin/sh grep 'JIRA' "$1" || echo "Commit message missing JIRA" only echoes but does not block commit. #!/bin/sh if grep -q 'JIRA' "$1"; then exit 1 fi blocks if 'JIRA' is present (wrong logic). #!/bin/sh echo "Checking commit message for JIRA" just echoes without checks.

4. Final Answer:

   #!/bin/sh if ! grep -q 'JIRA' "$1"; then echo "Commit message must include 'JIRA'." exit 1 fi -> Option C

5. Quick Check:

   Exit 1 if 'JIRA' missing blocks commit [OK]

Hint: Use commit-msg hook with exit 1 to block bad messages [OK]

Common Mistakes:

• Not exiting with non-zero to block commit
• Checking for presence instead of absence
• Only printing message without blocking