There are examples how to automatically deploy Jekyll site build using Git’s post-update or post-receive hooks which are server-side hooks.

I think it’s much more simple to use pre-push client-side (executes on your desktop) hook to automatically push a new site build to Github Pages before pushing to your Jekyll project repository.

Example:

I have my Jekyll blog repository blog hosted on a private Bitbucket repo. As a webhosting for my compiled version of a blog $ bundle exec jekyll build I use github-pages (repo vifreefly.github.io).

When I pushing a new commit (for example added new post under _posts/ directory) to remote blog origin, I want first to automatically build website (_site/ folder which stores compiled build by default) and push this build to vfreefly.github.io.

It’s easy to implement using pre-push git hook:

#!/bin/bash
# copy this to `.git/hooks/pre-push` hook file and make it executable: `$ chmod +x pre-push`

echo "> Hook started"

# Build a website to a standard _site directory
bundle exec jekyll build

# cd to the build folder
cd _site

# Init a new git repo inside `_site/` if it doesn't exists
if [ ! -d ".git" ]; then
  git init
fi

if [[ ! $(git remote) ]]; then
  # Add your github-pages repo (example https://github.com/vifreefly/vifreefly.github.io.git)
  # as origin for `_site` if it's not added yet:
  git remote add origin https://github.com/vifreefly/vifreefly.github.io.git
  # and push build to the github-pages repo with --force
  git add . && git commit -m "Build" && git push -u -f origin master
else
  # Push build to the github-pages repo with --force
  git add . && git commit -m "Build" && git push -f origin master
fi

echo "< Hook finished"

With this hook, when I’m doing $ git push origin master at Jekyll blog repository, a new build of a website pushes to Github Pages as well.

Also, you can use pre-push hook to push your blog to AWS S3 instead of github-pages for example.