pre-commit hook in Git - Mini Project: Build & Apply

Create a Git Pre-commit Hook to Check Commit Messages

📖 Scenario: You are working on a team project using Git. Your team wants to make sure every commit message starts with a capital letter and is at least 10 characters long. To help everyone follow this rule automatically, you will create a Git pre-commit hook script.

🎯 Goal: Build a Git pre-commit hook script that checks the commit message before the commit is saved. If the message does not start with a capital letter or is shorter than 10 characters, the commit will be stopped with a clear message.

📋 What You'll Learn

Create a pre-commit hook script file in the .git/hooks directory

Add a configuration variable to set the minimum commit message length

Write the core logic to check the commit message format

Print a message to allow or block the commit based on the check

💡 Why This Matters

🌍 Real World

Teams use pre-commit hooks to enforce commit message standards automatically, improving code history clarity.

💼 Career

Knowing how to write Git hooks is useful for DevOps engineers and developers to automate quality checks in version control.

1

Create the pre-commit hook script file

Create a file called .git/hooks/pre-commit and add the first line #!/bin/sh to specify the shell interpreter.

Git

# Create the pre-commit hook file and add the shebang line
# Your code here

Need a hint?

The first line of a shell script should be #!/bin/sh to tell Git how to run it.

2

Add a minimum length configuration variable

Inside the pre-commit script, create a variable called MIN_LENGTH and set it to 10 to define the minimum commit message length.

Git

#!/bin/sh
# Set minimum commit message length
# Your code here

Need a hint?

Use MIN_LENGTH=10 to store the minimum length number.

3

Write the logic to check the commit message

Add code to read the commit message from .git/COMMIT_EDITMSG into a variable called MSG. Then check if the first character is uppercase and if the message length is at least $MIN_LENGTH. If either check fails, print Commit message invalid and exit with status 1 to block the commit.

Git

#!/bin/sh
MIN_LENGTH=10
# Read commit message and check format
# Your code here

Need a hint?

Use head -n1 .git/COMMIT_EDITMSG to get the first line of the commit message. Use shell string length and grep to check conditions.

4

Print success message if commit message is valid

At the end of the script, add a line to print Commit message valid and exit with status 0 to allow the commit.

Git

#!/bin/sh
MIN_LENGTH=10
MSG=$(head -n1 .git/COMMIT_EDITMSG)
FIRST_CHAR=$(printf "%s" "$MSG" | cut -c1)
MSG_LENGTH=${#MSG}
if ! printf "%s" "$FIRST_CHAR" | grep -q '^[A-Z]'; then
  echo "Commit message invalid: first letter must be uppercase"
  exit 1
fi
if [ "$MSG_LENGTH" -lt "$MIN_LENGTH" ]; then
  echo "Commit message invalid: message must be at least $MIN_LENGTH characters"
  exit 1
fi
# Print success message and exit
# Your code here

Need a hint?

Use echo to print the success message and exit 0 to allow the commit.