Set Up Pre-Commit Hooks

Set Up Pre-Commit Hooks

Pre-commit hooks are scripts that run automatically before each commit. This guide will show you how to set up and use pre-commit hooks to enforce code quality and consistency.

What You’ll Learn

• Creating hooks
• Common hooks
• Best practices
• Troubleshooting
• Advanced usage

Implementation Steps

1. Basic Setup

   # Create hooks directory
   mkdir -p .git/hooks
   
   # Create pre-commit hook
   touch .git/hooks/pre-commit
   chmod +x .git/hooks/pre-commit
   

   • Set up directory
   • Create hook
   • Set permissions
   • Test hook

2. Simple Hook

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Run tests
   npm test
   
   # Check linting
   npm run lint
   
   # Exit with error if any check fails
   if [ $? -ne 0 ]; then
     echo "Tests or linting failed. Commit aborted."
     exit 1
   fi
   

   • Write script
   • Add checks
   • Handle errors
   • Test functionality

3. Common Checks

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Check for debug statements
   if git diff --cached | grep -i "console.log"; then
     echo "Error: console.log statements found"
     exit 1
   fi
   
   # Check file size
   if git diff --cached --name-only | xargs ls -l | awk '{sum+=$5} END {if(sum>1000000) exit 1}'; then
     echo "Error: Files too large"
     exit 1
   fi
   

   • Add checks
   • Set limits
   • Handle errors
   • Test hooks

4. Advanced Setup

   # Install pre-commit framework
   pip install pre-commit
   
   # Create config
   touch .pre-commit-config.yaml
   

   • Use framework
   • Configure hooks
   • Set up checks
   • Test setup

Best Practices

1. Hook Design

   • Keep it simple
   • Fail fast
   • Clear messages
   • Handle errors

2. Performance

   • Optimize checks
   • Cache results
   • Skip when needed
   • Monitor time

3. Maintenance

   • Document hooks
   • Version control
   • Regular updates
   • Team review

4. Security

   • Validate input
   • Check permissions
   • Safe execution
   • Monitor access

Common Use Cases

1. Code Quality

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Run linter
   npm run lint
   
   # Run tests
   npm test
   
   # Check formatting
   npm run format
   

2. File Checks

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Check file extensions
   for file in $(git diff --cached --name-only); do
     if [[ $file == *.md ]]; then
       # Check markdown
       markdownlint $file
     fi
   done
   

3. Security Checks

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Check for secrets
   if git diff --cached | grep -i "password\|secret\|key"; then
     echo "Error: Potential secrets found"
     exit 1
   fi
   

4. Documentation

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Check for TODO comments
   if git diff --cached | grep -i "TODO"; then
     echo "Warning: TODO comments found"
   fi
   

Advanced Usage

1. Framework Integration

   # .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
         - id: check-added-large-files
   

2. Custom Hooks

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Run custom checks
   ./scripts/custom-check.sh
   
   # Run specific tests
   npm run test:changed
   

3. Conditional Execution

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Skip hooks if needed
   if [ -f .skip-hooks ]; then
     exit 0
   fi
   
   # Run checks
   npm test
   

4. Team Hooks

   #!/bin/bash
   # .git/hooks/pre-commit
   
   # Check team standards
   ./scripts/team-standards.sh
   
   # Run team checks
   npm run team:check
   

Common Issues and Solutions

1. Hook Not Running

   # Check permissions
   chmod +x .git/hooks/pre-commit
   
   # Verify hook
   git commit --dry-run
   

2. Performance Issues

   # Add caching
   if [ -f .hook-cache ] && [ $(git diff --cached --name-only | md5sum) = $(cat .hook-cache) ]; then
     exit 0
   fi
   

3. False Positives

   # Add exceptions
   if [[ $file == *"test"* ]]; then
     # Skip checks for test files
     exit 0
   fi
   

Conclusion

Pre-commit hooks are powerful tools. Remember to:

• Start simple
• Test thoroughly
• Document well
• Monitor performance
• Follow best practices

Next Steps

After mastering pre-commit hooks, consider:

• Learning Git workflows
• Exploring CI/CD
• Understanding Git internals
• Setting up automated testing