Git Notes

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Git Hooks - Automate Workflows with Git Events

Learn to use Git hooks for automating code quality checks, commit message validation, pre-push testing, and deployment triggers. Covers client-side and server-side hooks.

Git hooks are scripts that run automatically at specific points in the Git workflow. They enable automation for code quality checks, commit message validation, testing, and deployment.

What Are Git Hooks?

Hooks are executable scripts stored in .git/hooks/ that Git triggers during operations like committing, pushing, or merging.

│ git commit	│
│ pre-commit	prepare-commit-msg → │
│ commit-msg	post-commit │
│ git push	│
│ pre-push	(remote) pre-receive → │
│ update	post-receive │
│ git merge	│
│ pre-merge-commit	post-merge │

Client-Side Hooks

pre-commit

Runs before the commit message editor opens. Use for linting and formatting:

Example

#!/bin/sh # .git/hooks/pre-commit # Run ESLint on staged files STAGED_FILES=$(git diff --cached --name-only --diff-filter=ACM | grep -E "\.(js|ts|jsx|tsx)$") if [ -n "$STAGED_FILES" ]; then echo "Running ESLint..." npx eslint $STAGED_FILES if [ $? -ne 0 ]; then echo "❌ ESLint failed. Fix errors before committing." exit 1 fi fi echo "✅ Pre-commit checks passed" exit 0

commit-msg

Validates the commit message format:

bash example

#!/bin/sh
# .git/hooks/commit-msg

COMMIT_MSG_FILE=$1
COMMIT_MSG=$(cat "$COMMIT_MSG_FILE")

# Enforce conventional commits format
PATTERN="^(feat|fix|docs|style|refactor|test|chore)(\(.+\))?: .{1,72}$"

if ! echo "$COMMIT_MSG" | grep -qE "$PATTERN"; then
    echo "❌ Invalid commit message format!"
    echo ""
    echo "Expected: type(scope): description"
    echo "Types: feat, fix, docs, style, refactor, test, chore"
    echo ""
    echo "Example: feat(auth): add login functionality"
    echo "Your message: $COMMIT_MSG"
    exit 1
fi

echo "✅ Commit message format valid"
exit 0

pre-push

Runs before pushing to remote. Use for running tests:

Example

#!/bin/sh # .git/hooks/pre-push echo "Running tests before push..." npm test if [ $? -ne 0 ]; then echo "❌ Tests failed! Push aborted." echo "Fix failing tests before pushing." exit 1 fi echo "✅ All tests passed. Pushing..." exit 0

prepare-commit-msg

Modifies the default commit message:

Example

#!/bin/sh # .git/hooks/prepare-commit-msg COMMIT_MSG_FILE=$1 BRANCH_NAME=$(git symbolic-ref --short HEAD) # Extract ticket number from branch name TICKET=$(echo "$BRANCH_NAME" | grep -oE "[A-Z]+-[0-9]+") if [ -n "$TICKET" ]; then # Prepend ticket number to commit message sed -i.bak "1s/^/[$TICKET] /" "$COMMIT_MSG_FILE" fi

post-commit

Runs after a commit is created (cannot prevent the commit):

bash example

#!/bin/sh
# .git/hooks/post-commit

echo "✅ Commit created successfully!"
echo "Commit: $(git log --oneline -1)"

Server-Side Hooks

pre-receive

Runs on the remote server before accepting a push:

Example

#!/bin/sh # hooks/pre-receive (on server) while read oldrev newrev refname; do # Prevent force-push to main if [ "$refname" = "refs/heads/main" ]; then if [ "$oldrev" != "0000000000000000000000000000000000000000" ]; then MERGE_BASE=$(git merge-base $oldrev $newrev) if [ "$MERGE_BASE" != "$oldrev" ]; then echo "❌ Force push to main is not allowed!" exit 1 fi fi fi done exit 0

post-receive

Runs after a push is accepted. Used for deployment triggers:

Example

#!/bin/sh # hooks/post-receive (on server) while read oldrev newrev refname; do if [ "$refname" = "refs/heads/main" ]; then echo "Deploying to production..." GIT_WORK_TREE=/var/www/app git checkout -f main cd /var/www/app && npm install && npm run build sudo systemctl restart app echo "✅ Deployment complete!" fi done

Setting Up Hooks

Manual Setup

bash example

# Navigate to hooks directory
cd .git/hooks

# Create a hook (example: pre-commit)
cat > pre-commit << 'EOF'
#!/bin/sh
echo "Running pre-commit hook..."
npm run lint
EOF

# Make it executable
chmod +x pre-commit

Using Husky (Recommended for Teams)

Husky manages Git hooks through package.json, so hooks are shared with the team:

bash example

# Install Husky
npm install --save-dev husky

# Initialize Husky
npx husky init

bash example

# Create a pre-commit hook
echo "npm run lint" > .husky/pre-commit

# Create a commit-msg hook
echo 'npx commitlint --edit $1' > .husky/commit-msg

json example

// package.json
{
  "scripts": {
    "prepare": "husky",
    "lint": "eslint src/",
    "test": "jest"
  }
}

Using lint-staged

Run linters only on staged files for speed:

bash example

npm install --save-dev lint-staged

Example

// package.json { "lint-staged": { "*.{js,ts,jsx,tsx}": ["eslint --fix", "prettier --write"], "*.{css,scss}": ["stylelint --fix"], "*.{json,md}": ["prettier --write"] } }

bash example

# .husky/pre-commit
npx lint-staged

All Available Hooks

Hook	Trigger	Can Abort?
pre-commit	Before commit	✅ Yes
prepare-commit-msg	After default msg created	✅ Yes
commit-msg	After user enters message	✅ Yes
post-commit	After commit created	❌ No
pre-rebase	Before rebase starts	✅ Yes
post-rewrite	After commit rewrite (amend/rebase)	❌ No
pre-push	Before push to remote	✅ Yes
pre-merge-commit	Before merge commit	✅ Yes
post-merge	After merge completes	❌ No
post-checkout	After checkout/switch	❌ No

Bypassing Hooks

bash example

# Skip pre-commit and commit-msg hooks
git commit --no-verify -m "Emergency fix"
# or
git commit -n -m "Emergency fix"

# Skip pre-push hook
git push --no-verify

Interview Questions

What are Git hooks and where are they stored?

Git hooks are scripts that run automatically at specific points in the Git workflow. They are stored in the .git/hooks/ directory of each repository. Hooks can automate tasks like linting, testing, and deployment.

How do you share hooks with your team?

Use tools like Husky that store hook configurations in the repository (e.g., .husky/ directory). Since .git/hooks/ is not tracked, you need a mechanism to install hooks when teammates clone the repo.

What is the difference between pre-commit and commit-msg hooks?

pre-commit runs before the commit message editor opens and is used for code checks (linting, formatting). commit-msg runs after the message is written and validates the commit message format.

How do you bypass a Git hook?

Use the --no-verify or -n flag: git commit --no-verify. This skips pre-commit and commit-msg hooks. Use sparingly for emergencies.

What is the difference between client-side and server-side hooks?

Client-side hooks run on the developer machine (pre-commit, pre-push) and can be bypassed. Server-side hooks run on the remote (pre-receive, post-receive) and cannot be bypassed by clients.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for Git Hooks - Automate Workflows with Git Events.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Git & GitHub topic.

Search Terms

git-github, git & github, git, github, advanced, hooks, git hooks - automate workflows with git events

Related Git & GitHub Topics

Continue learning this concept

Advanced GitGit Bisect - Find Bugs with Binary SearchLearn how to use git bisect to efficiently find the commit that introduced a bug using binary search. Master automated bisect with scripts and practical debugging workflows.Advanced GitGit Cherry-Pick - Apply Specific Commits to Any BranchLearn how to use git cherry-pick to apply individual commits from one branch to another. Master cherry-pick options, conflict resolution, and best practices.Advanced GitGit Internals - Understanding How Git Works Under the HoodDeep dive into Git internals including objects (blobs, trees, commits), the SHA-1 hash system, packfiles, refs, and how Git stores data as a content-addressable filesystem.Advanced GitGit Stash - Temporarily Save Uncommitted ChangesMaster git stash to save work-in-progress changes without committing. Learn stash operations, named stashes, partial stashing, and workflow patterns.Advanced GitGit Submodules - Manage External Dependencies as Git ReposLearn how to use Git submodules to include external repositories within your project. Cover adding, updating, cloning with submodules, and alternatives.Advanced GitGit Tag - Mark Important Points in HistoryLearn how to create, list, and manage Git tags for releases and milestones. Understand lightweight vs annotated tags, semantic versioning, and tag workflows.

PreviousGit Cherry-Pick - Apply Specific Commits to Any Branch NextGit Internals - Understanding How Git Works Under the Hood

Git Notes

Git Hooks - Automate Workflows with Git Events

Learn to use Git hooks for automating code quality checks, commit message validation, pre-push testing, and deployment triggers. Covers client-side and server-side hooks.

Git hooks are scripts that run automatically at specific points in the Git workflow. They enable automation for code quality checks, commit message validation, testing, and deployment.

What Are Git Hooks?

Hooks are executable scripts stored in .git/hooks/ that Git triggers during operations like committing, pushing, or merging.

│ git commit	│
│ pre-commit	prepare-commit-msg → │
│ commit-msg	post-commit │
│ git push	│
│ pre-push	(remote) pre-receive → │
│ update	post-receive │
│ git merge	│
│ pre-merge-commit	post-merge │

Client-Side Hooks

pre-commit

Runs before the commit message editor opens. Use for linting and formatting:

Example

commit-msg

Validates the commit message format:

bash example

#!/bin/sh
# .git/hooks/commit-msg

COMMIT_MSG_FILE=$1
COMMIT_MSG=$(cat "$COMMIT_MSG_FILE")

# Enforce conventional commits format
PATTERN="^(feat|fix|docs|style|refactor|test|chore)(\(.+\))?: .{1,72}$"

if ! echo "$COMMIT_MSG" | grep -qE "$PATTERN"; then
    echo "❌ Invalid commit message format!"
    echo ""
    echo "Expected: type(scope): description"
    echo "Types: feat, fix, docs, style, refactor, test, chore"
    echo ""
    echo "Example: feat(auth): add login functionality"
    echo "Your message: $COMMIT_MSG"
    exit 1
fi

echo "✅ Commit message format valid"
exit 0

pre-push

Runs before pushing to remote. Use for running tests:

Example

prepare-commit-msg

Modifies the default commit message:

Example

post-commit

Runs after a commit is created (cannot prevent the commit):

bash example

#!/bin/sh
# .git/hooks/post-commit

echo "✅ Commit created successfully!"
echo "Commit: $(git log --oneline -1)"

Server-Side Hooks

pre-receive

Runs on the remote server before accepting a push:

Example

post-receive

Runs after a push is accepted. Used for deployment triggers:

Example

Setting Up Hooks

Manual Setup

bash example

# Navigate to hooks directory
cd .git/hooks

# Create a hook (example: pre-commit)
cat > pre-commit << 'EOF'
#!/bin/sh
echo "Running pre-commit hook..."
npm run lint
EOF

# Make it executable
chmod +x pre-commit

Using Husky (Recommended for Teams)

Husky manages Git hooks through package.json, so hooks are shared with the team:

bash example

# Install Husky
npm install --save-dev husky

# Initialize Husky
npx husky init

bash example

# Create a pre-commit hook
echo "npm run lint" > .husky/pre-commit

# Create a commit-msg hook
echo 'npx commitlint --edit $1' > .husky/commit-msg

json example

// package.json
{
  "scripts": {
    "prepare": "husky",
    "lint": "eslint src/",
    "test": "jest"
  }
}

Using lint-staged

Run linters only on staged files for speed:

bash example

npm install --save-dev lint-staged

Example

// package.json { "lint-staged": { "*.{js,ts,jsx,tsx}": ["eslint --fix", "prettier --write"], "*.{css,scss}": ["stylelint --fix"], "*.{json,md}": ["prettier --write"] } }

bash example

# .husky/pre-commit
npx lint-staged

All Available Hooks

Hook	Trigger	Can Abort?
pre-commit	Before commit	✅ Yes
prepare-commit-msg	After default msg created	✅ Yes
commit-msg	After user enters message	✅ Yes
post-commit	After commit created	❌ No
pre-rebase	Before rebase starts	✅ Yes
post-rewrite	After commit rewrite (amend/rebase)	❌ No
pre-push	Before push to remote	✅ Yes
pre-merge-commit	Before merge commit	✅ Yes
post-merge	After merge completes	❌ No
post-checkout	After checkout/switch	❌ No

Bypassing Hooks

bash example

# Skip pre-commit and commit-msg hooks
git commit --no-verify -m "Emergency fix"
# or
git commit -n -m "Emergency fix"

# Skip pre-push hook
git push --no-verify

Interview Questions

What are Git hooks and where are they stored?

How do you share hooks with your team?

What is the difference between pre-commit and commit-msg hooks?

pre-commit runs before the commit message editor opens and is used for code checks (linting, formatting). commit-msg runs after the message is written and validates the commit message format.

How do you bypass a Git hook?

Use the --no-verify or -n flag: git commit --no-verify. This skips pre-commit and commit-msg hooks. Use sparingly for emergencies.

What is the difference between client-side and server-side hooks?

Client-side hooks run on the developer machine (pre-commit, pre-push) and can be bypassed. Server-side hooks run on the remote (pre-receive, post-receive) and cannot be bypassed by clients.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for Git Hooks - Automate Workflows with Git Events.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Git & GitHub topic.

Search Terms

git-github, git & github, git, github, advanced, hooks, git hooks - automate workflows with git events

Related Git & GitHub Topics

Continue learning this concept

PreviousGit Cherry-Pick - Apply Specific Commits to Any Branch NextGit Internals - Understanding How Git Works Under the Hood