Overview
Git hooks are an invaluable resource for teams looking to automate and streamline their version control workflows. By optimizing git hooks, you can ensure code quality, enforce policies, and even trigger build scripts. One particular type of hook, the update hook, is called by git-receive-pack on the remote repository, which happens when a git push is executed. In this guide, we’ll dive deep into git update hooks, outlining how to use them effectively, with practical examples and advanced use cases.
What are Git Update Hooks?
An update hook is a script in a git repository that is executed before a push is finally accepted. If this hook script exits with a non-zero status, the push is denied. This checking mechanism serves as an automated gatekeeper for new commits. Update hooks can perform a range of tasks, from verifying commit messages to code linting, and more.
Setting Up Your First Update Hook
To start using an update hook, you must place a script named ‘update’ in the .git/hooks directory of your repository. Since this script is not tracked by git, it exists only on the ‘central’ repository where you’re pushing your changes.
#!/bin/sh
# An example of a simple update hook script
refname="
3
oldrev="
2
newrev="
1
# Enforce that commit messages contain a JIRA issue ID
commit_regex='[A-Z]+-\d+'
error_msg="Error: Commit message does not reference a JIRA ticket."
while read oldrev newrev refname; do
if ! git log --max-count=1 --format=%B
2
newrev... | grep -qE "commit_regex"; then
echo "error_msg" >&2
exit 1
fi
done
exit 0
This script checks that commit messages contain a JIRA issue ID.
Automation with Update Hooks
Beyond commit message validation, update hooks can execute automated tests.
#!/bin/sh
# Run automated tests with an update hook
refname="
3
oldrev="
2
newrev="
1
# Temporary directory for checkout
TEMPDIR=
/tmp/update-hook-test-workdir
# Base directory of the repository
REPO_DIR=
$(git rev-parse --show-toplevel)
# Branch to be checked out
BRANCH_NAME=
${refname##refs/heads/}
# Function to perform cleanup
cleanup () {
rm -rf "TEMPDIR"
}
# Create temporary directory, checkout code, and run tests
mkdir -p "TEMPDIR" &&
cd "TEMPDIR" &&
git --work-tree="TEMPDIR" --git-dir="REPO_DIR/.git" checkout -f "BRANCH_NAME" &&
(your test command here...)
RESULT=
$?
cleanup
if [ "RESULT" -ne 0 ]; then
echo "Tests failed on branch BRANCH_NAME" >&2
exit 1
fi
exit 0
This script shows how to clone the repo into a temporary directory, checkout a specific branch, and run tests.
Best Practices
While they are powerful, update hooks can become a bottleneck if not managed properly. It’s essential to optimize them for performance and maintainability. Rely on logical snippets, document changes, and keep your team informed about the hooks present in the repository. Whenever you’re dealing with hooks executing heavy operations, ensure scripts are efficient and do not degrade the system’s performance.
For large projects, it’s efficient to encapsulate common logic in separate scripts and invoke them from the update hook.
Conclusion
Incorporating git update hooks into your workflow can be a game-changer in ensuring adherence to project guidelines and automated testing. As seen in the examples provided, from simple checks to complex test executions, there’s a variety of ways they can assist in maintaining code integrity. Use them wisely, always considering the impact on your development cycle.
