commit-msg hook for message validation in Git - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a commit-msg hook script

Given this commit-msg hook script, what will be the output if the commit message is "Fix bug in login"?

Git

#!/bin/sh
MESSAGE_FILE=$1
MESSAGE=$(cat "$MESSAGE_FILE")
if echo "$MESSAGE" | grep -qE '^\[JIRA-[0-9]+\]'; then
  exit 0
else
  echo "Error: Commit message must start with a JIRA ticket ID like [JIRA-123]"
  exit 1
fi

A Error: Commit message is too short

B No output, commit succeeds

C Syntax error in script

D Error: Commit message must start with a JIRA ticket ID like [JIRA-123]

💡 Hint

Check if the commit message starts with the required pattern.

The script checks if the commit message starts with a pattern like [JIRA-123]. Since "Fix bug in login" does not start with that, it prints the error and exits with failure.

🧠 Conceptual

intermediate

Purpose of commit-msg hook

What is the main purpose of a commit-msg hook in Git?

A To check and validate the commit message before allowing the commit

B To automatically push commits to remote repositories

C To merge branches after commit

D To delete untracked files before commit

💡 Hint

Think about what happens right after you write a commit message.

The commit-msg hook runs after you write a commit message and before the commit is finalized. It is used to validate or modify the commit message.

❓ Troubleshoot

advanced

Why does the commit-msg hook not run?

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

A The repository is not initialized

B The script file is not executable

C The hook script is named commit-msg.txt

D The commit message is empty

💡 Hint

Check file permissions for scripts in .git/hooks/

Git only runs hook scripts that have executable permissions. If the script is not executable, Git ignores it.

🔀 Workflow

advanced

Implementing commit-msg hook for multiple rules

You want a commit-msg hook that enforces these rules:
1. Commit message must start with [PROJ-123]
2. Commit message must be at least 15 characters long
Which script correctly implements both checks?

A

#!/bin/sh
MSG=$(cat "$1")
if ! echo "$MSG" | grep -qE '^\[PROJ-[0-9]+\]'; then
  echo "Error: Message must start with [PROJ-123]"
  exit 1
fi
if [ ${#MSG} -lt 15 ]; then
  echo "Error: Message must be at least 15 characters"
  exit 1
fi
exit 0

B

#!/bin/sh
MSG=$(cat "$1")
if echo "$MSG" | grep -qE '^\[PROJ-[0-9]+\]' || [ ${#MSG} -ge 15 ]; then
  exit 0
else
  echo "Error: Commit message invalid"
  exit 1
fi

C

#!/bin/sh
MSG=$(cat "$1")
if echo "$MSG" | grep -qE '^\[PROJ-[0-9]+\]' && [ ${#MSG} -ge 15 ]; then
  exit 1
else
  echo "Error: Commit message invalid"
  exit 0
fi

D

#!/bin/sh
MSG=$(cat "$1")
if ! echo "$MSG" | grep -qE '^\[PROJ-[0-9]+\]' || [ ${#MSG} -lt 15 ]; then
  echo "Error: Commit message invalid"
  exit 1
fi
exit 0

💡 Hint

Both conditions must be true to pass validation.

Option A checks each condition separately and exits with error if either fails. Other options have logic errors or inverted exit codes.

✅ Best Practice

expert

Best practice for sharing commit-msg hooks in a team

What is the best way to ensure all team members use the same commit-msg hook for message validation?

A Add the hook script to .gitignore so it is not tracked

B Ask each member to manually create the hook in their .git/hooks/ folder

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

D Use a global Git hook configured on each developer's machine

💡 Hint

Think about version controlling the hook and automating installation.

Git does not version control .git/hooks/, so storing hooks in the repo and copying them during setup ensures consistency. Global hooks are possible but less flexible for project-specific rules.