pre-commit hook in Git - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple pre-commit hook script

What will be the output when you try to commit with this pre-commit hook script in .git/hooks/pre-commit?

Git

#!/bin/sh

echo "Checking commit message length..."
MSG=$(head -n1 .git/COMMIT_EDITMSG)
LEN=$(echo -n "$MSG" | wc -c)
if [ $LEN -lt 10 ]; then
  echo "Commit message too short. Please write at least 10 characters."
  exit 1
fi
exit 0

A Commit is blocked with message: "Commit message too short. Please write at least 10 characters."

B Commit proceeds but prints "Commit message too short. Please write at least 10 characters."

C Commit is blocked with message: "Checking commit message length..." only

D Commit proceeds without any message

💡 Hint

Think about what happens if the commit message is shorter than 10 characters.

The script checks the first line of the commit message. If it is shorter than 10 characters, it prints an error and exits with status 1, blocking the commit.

🧠 Conceptual

intermediate

Purpose of pre-commit hooks in Git

Which of the following best describes the main purpose of a pre-commit hook in Git?

A To run checks or scripts before a commit is finalized

B To automatically merge branches before committing

C To push commits to the remote repository automatically

D To delete untracked files before committing

💡 Hint

Think about what happens right before a commit is saved.

Pre-commit hooks run scripts or checks before the commit is finalized, allowing you to prevent bad commits or enforce rules.

❓ Troubleshoot

advanced

Why does the pre-commit hook not run?

You created a pre-commit hook script in .git/hooks/pre-commit but it does not run when committing. What is the most likely reason?

A The commit message is empty

B The script file is named <code>pre-commit.sh</code> instead of <code>pre-commit</code>

C The script file is missing execute permissions

D The Git repository is not initialized

💡 Hint

Check the file permissions of the hook script.

Git only runs hook scripts that have execute permissions. Without it, the script is ignored.

🔀 Workflow

advanced

Order of operations in a pre-commit hook script

You want to create a pre-commit hook that first checks code style with flake8 and then runs tests with pytest. Which order of commands in the script ensures the commit is blocked if either check fails?

Git

#!/bin/sh

# Commands to run

A

2
3
1

B

1
2
3

C

3
2
1

D

2
1
3

💡 Hint

The script should stop at the first failure to block the commit.

Running flake8 first and then pytest ensures style is checked before tests. If either fails, the script exits with non-zero status, blocking the commit.

✅ Best Practice

expert

Best practice for sharing pre-commit hooks across a team

What is the best practice to ensure all team members use the same pre-commit hooks without manually copying scripts into their .git/hooks directories?

A Add the hook scripts to the repository and instruct everyone to copy them manually

B Use a tool like <code>pre-commit</code> framework to manage hooks via configuration files

C Commit the <code>.git/hooks</code> directory to the repository

D Send the hook scripts by email to each team member

💡 Hint

Think about automation and consistency for teams.

The pre-commit framework allows defining hooks in a config file that is version controlled, so all team members can install and run the same hooks easily.