Deploy a generated GitHub page (`_site` subfolder)

deploy.sh

#!/usr/bin/env bash

# Configuration
# The remote target branch name needs to be
# 1. DIFFERENT from the local development branch
# 2. Set as the default branch name on GitHub
remote_target_branch=master
generated_contents_dir=_site

get-working-branch() {
    git status | head -n 1 | awk '{ print $NF }'
}

cleanup() {
    git checkout "$local_working_branch"
}

# Ensure that the working branch is put back the way it was.
trap cleanup EXIT

# In the following
#
# * we create a new branch with the remote target’s name,
# * add the generated contents (`_site` directory),
# * commit the contents, and
# * remove everything but the generated contents, such that the `_site`
#   directory becomes the root directory (similar to `mv _site .`).
# * Finally, we push the commit to the remote.

remote_name="$(git remote | head -n 1)"
local_working_branch="$(get-working-branch)"
# Ensure that the target branch is cleared, if it already existed.
git branch --delete --force "$remote_target_branch"
git checkout -b "$remote_target_branch"

git add --force "$generated_contents_dir"
git commit --message "New version $(date)"
git filter-branch --subdirectory-filter "$generated_contents_dir/" --force

git push "$remote_name" "$remote_target_branch" --force

# vim: ft=sh