Git Pre-commit Hook: Real-World Use Cases

Git hooks are powerful automation features that allow you to run scripts before or after Git events. Among these, the pre-commit hook is especially useful in enforcing standards before changes are committed.

Below is a simple example of a pre-commit hook that blocks committing empty files:

#!/bin/bash

# Loop through all staged files
for file in $(git diff --cached --name-only)
do
  # If the file is empty, block the commit
  if [ ! -s "$file" ]; then
    echo "❌ File '$file' is empty. Please add some content before committing."
    exit 1
  fi
done

# If all files are valid, allow the commit
exit 0

This is just the beginning! A pre-commit hook can do much more to improve code quality, maintain security, and enforce team practices.

🚀 Where Can You Use Pre-commit Hook? (Real-World Examples)

1. ✅ Code Formatting Check

Ensure that code is properly formatted before committing.

Python: black, flake8
JavaScript: prettier, eslint

prettier --check .

2. 🔍 Linting (Code Rule Checks)

Prevent syntax errors or bad coding practices from being committed.

eslint . --max-warnings=0

3. 🔐 Secrets Scanner

Detect and prevent committing passwords, tokens, or AWS keys.

detect-secrets scan

4. 📜 Commit Message Format Checker

Enforce a specific commit message format, such as Conventional Commits.

if ! grep -qE "^(feat|fix|docs):" "$1"; then
  echo "❌ Commit message must start with feat:, fix:, or docs:"
  exit 1
fi

5. 🧪 Run Unit Tests

Automatically run tests before a commit to avoid pushing broken code.

npm test
# or
pytest

6. 📂 Large File Blocker

Block accidentally committed large files (e.g., 50MB+):

for file in $(git diff --cached --name-only); do
  if [ $(stat -c%s "$file") -gt 50000000 ]; then
    echo "❌ File '$file' is too large!"
    exit 1
  fi
done

7. 🧹 Auto File Cleanup

Automatically remove trailing spaces or extra newlines:

sed -i 's/[ \t]*$//' "$file"  # remove trailing spaces

🧰 Manage Pre-commit Hooks Easily

For complex workflows, use the pre-commit framework. It's a Python-based tool that simplifies hook management.

Example .pre-commit-config.yaml:

repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.4.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml

To activate it:

pre-commit install

📦 Summary Table

Use Case	Benefit
Code Format Check	Clean and consistent code
Linting	Avoid syntax/style issues
Secrets Detection	Prevent leaking credentials
Commit Message Format	Enforce team standards
Run Tests	Catch bugs early
File Size Check	Avoid accidentally committing big files
Auto Cleanup	Clean code without manual work

Final Thoughts

The pre-commit hook is one of the most practical ways to automate checks and enforce policies before a commit is made. By incorporating these hooks, you reduce the risk of introducing errors, maintain consistency, and streamline collaboration across teams.

Add this to your Git workflow today and elevate your development standards!

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