deploy.sh

#!/usr/bin/env bash
set -o errexit #abort if any command fails

main() {
	deploy_directory="html/"
	deploy_branch="gh-pages"

	#repository to deploy to. must be readable and writable.
	repo=${GIT_DEPLOY_REPO:-origin}
	
	# Parse arg flags
	while : ; do
		if [[ $1 = "-v" || $1 = "--verbose" ]]; then
			verbose=true
			shift
		elif [[ $1 = "-e" || $1 = "--allow-empty" ]]; then
			allow_empty=true
			shift
		else
			break
		fi
	done
	
	enable_expanded_output

	if ! git diff --exit-code --quiet --cached; then
		echo Aborting due to uncommitted changes in the index >&2
		return 1
	fi

	commit_title=`git log -n 1 --format="%s" HEAD`
	commit_hash=` git log -n 1 --format="%H" HEAD`
	previous_branch=`git rev-parse --abbrev-ref HEAD`

	if [ ! -d "$deploy_directory" ]; then
		echo "Deploy directory '$deploy_directory' does not exist. Aborting." >&2
		return 1
	fi

	if [[ -z `ls -A "$deploy_directory" 2> /dev/null` && -z $allow_empty ]]; then
		echo "Deploy directory '$deploy_directory' is empty. Aborting. If you're sure you want to deploy an empty tree, use the --allow-empty / -e flag." >&2
		return 1
	fi

	if git ls-remote --exit-code $repo "refs/heads/$deploy_branch" ; then
		# deploy_branch exists in $repo; make sure we have the latest version
		
		disable_expanded_output
		git fetch --force $repo $deploy_branch:$deploy_branch
		enable_expanded_output
	fi

	# check if deploy_branch exists locally
	if git show-ref --verify --quiet "refs/heads/$deploy_branch"
	then incremental_deploy
	else initial_deploy
	fi

	restore_head
}

initial_deploy() {
	git --work-tree "$deploy_directory" checkout --orphan $deploy_branch
	git --work-tree "$deploy_directory" add --all
	commit+push
}

incremental_deploy() {
	#make deploy_branch the current branch
	git symbolic-ref HEAD refs/heads/$deploy_branch
	#put the previously committed contents of deploy_branch into the index
	git --work-tree "$deploy_directory" reset --mixed --quiet
	git --work-tree "$deploy_directory" add --all

	set +o errexit
	diff=$(git --work-tree "$deploy_directory" diff --exit-code --quiet HEAD --)$?
	set -o errexit
	case $diff in
		0) echo No changes to files in $deploy_directory. Skipping commit.;;
		1) commit+push;;
		*)
			echo git diff exited with code $diff. Aborting. Staying on branch $deploy_branch so you can debug. To switch back to master, use: git symbolic-ref HEAD refs/heads/master && git reset --mixed >&2
			return $diff
			;;
	esac
}

commit+push() {
	git --work-tree "$deploy_directory" commit -m \
		"publish: $commit_title"$'\n\n'"generated from commit $commit_hash"

	disable_expanded_output
	#--quiet is important here to avoid outputting the repo URL, which may contain a secret token
	git push --quiet $repo $deploy_branch
	enable_expanded_output
}

#echo expanded commands as they are executed (for debugging)
enable_expanded_output() {
	if [ $verbose ]; then
		set -o xtrace
		set +o verbose
	fi
}

#this is used to avoid outputting the repo URL, which may contain a secret token
disable_expanded_output() {
	if [ $verbose ]; then
		set +o xtrace
		set -o verbose
	fi
}

restore_head() {
	if [[ $previous_branch = "HEAD" ]]; then
		#we weren't on any branch before, so just set HEAD back to the commit it was on
		git update-ref --no-deref HEAD $commit_hash $deploy_branch
	else
		git symbolic-ref HEAD refs/heads/$previous_branch
	fi
	
	git reset --mixed
}

filter() {
	sed -e "s|$repo|\$repo|g"
}

sanitize() {
	"$@" 2> >(filter 1>&2) | filter
}

[[ $1 = --source-only ]] || main "$@"