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Git Hooks in Practice — Automating Code Quality with pre-commit

Explains how to write pre-commit, commit-msg, and pre-push hooks yourself, or use the pre-commit framework to automatically run linting, formatting, and tests before a commit.

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Contents
  1. Git Hooks Location
  2. Writing a pre-commit Hook Yourself
  3. commit-msg Hook — Enforcing Commit Message Format
  4. pre-push Hook — Push Only After Tests Pass
  5. The pre-commit Framework (Recommended)
  6. Bypassing Hooks (Emergencies Only)

Git Hooks Location

Bash
ls .git/hooks/
# pre-commit.sample, commit-msg.sample, pre-push.sample ...

Hook files must be saved without an extension and granted execute permission.

Writing a pre-commit Hook Yourself

Bash
# .git/hooks/pre-commit
#!/usr/bin/env bash
set -e

echo "Running pre-commit checks..."

# ESLint
if ! npx eslint --max-warnings 0 $(git diff --cached --name-only --diff-filter=ACM | grep -E '\.(js|ts)$'); then
  echo "ESLint failed. Fix errors before committing."
  exit 1
fi

# Prettier check
if ! npx prettier --check $(git diff --cached --name-only --diff-filter=ACM | grep -E '\.(js|ts|json|css)$'); then
  echo "Prettier check failed. Run: npx prettier --write ."
  exit 1
fi

echo "Pre-commit checks passed."
Bash
chmod +x .git/hooks/pre-commit

commit-msg Hook — Enforcing Commit Message Format

Bash
# .git/hooks/commit-msg
#!/usr/bin/env bash
COMMIT_MSG_FILE="$1"
COMMIT_MSG=$(cat "$COMMIT_MSG_FILE")

# Conventional Commits
PATTERN='^(feat|fix|docs|style|refactor|test|chore|perf|ci)(\(.+\))?: .{1,72}'
if ! echo "$COMMIT_MSG" | grep -qE "$PATTERN"; then
 echo "❌ when "
 echo " : feat: "
 echo " : feat|fix|docs|style|refactor|test|chore|perf|ci"
  exit 1
fi

pre-push Hook — Push Only After Tests Pass

Bash
# .git/hooks/pre-push
#!/usr/bin/env bash
set -e

echo "Running tests before push..."
npm test -- --passWithNoTests

echo "All tests passed. Pushing..."

To share hooks across a team, use the pre-commit framework.

Bash
pip install pre-commit
YAML
# .pre-commit-config.yaml
repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.5.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml
      - id: check-json
      - id: check-merge-conflict

  - repo: https://github.com/pre-commit/mirrors-eslint
    rev: v8.56.0
    hooks:
      - id: eslint
        files: \.(js|ts)$
        additional_dependencies:
          - eslint@8.56.0

  - repo: https://github.com/pre-commit/mirrors-prettier
    rev: v3.1.0
    hooks:
      - id: prettier
Bash
# ( run)
pre-commit install
pre-commit install --hook-type commit-msg

# run
pre-commit run --all-files

# file
pre-commit run --files src/index.ts

Bypassing Hooks (Emergencies Only)

Bash
git commit --no-verify -m "hotfix: "
git push --no-verify

Do not use this routinely. Agree on team rules so that bypasses leave an audit trail.

#git#git-hooks#pre-commit
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