deploy.sh

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

deploy_directory=public
deploy_branch=gh-pages

#if no user identity is already set in the current git environment, use this:
default_username=deploy.sh
default_email=

#repository to deploy to. must be readable and writable.
repo=origin

# Parse arg flags
while : ; do
	if [[ $1 = "-v" || $1 = "--verbose" ]]; then
		verbose=true
		shift
	elif [[ $1 = "-s" || $1 = "--setup" ]]; then
		setup=true
		shift
	elif [[ $1 = "-e" || $1 = "--allow-empty" ]]; then
		allow_empty=true
		shift
	else
		break
	fi
done

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

enable_expanded_output

function set_user_id {
	if [[ -z `git config user.name` ]]; then
		git config user.name "$default_username"
	fi
	if [[ -z `git config user.email` ]]; then
		git config user.email "$default_email"
	fi
}

function 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
}

if ! git diff --exit-code --quiet --cached; then
	echo Aborting due to uncommitted changes in the index >&2
	exit 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 [ $setup ]; then
	mkdir -p "$deploy_directory"
	git --work-tree "$deploy_directory" checkout --orphan $deploy_branch
	git --work-tree "$deploy_directory" rm -r "*"
	git --work-tree "$deploy_directory" add --all
	git --work-tree "$deploy_directory" commit -m "initial publish"$'\n\n'"generated from commit $commit_hash"
	git push $repo $deploy_branch
	restore_head
	exit
fi

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

disable_expanded_output
git fetch --force $repo $deploy_branch:$deploy_branch
enable_expanded_output

#make deploy_branch the current branch
git symbolic-ref HEAD refs/heads/$deploy_branch

#put the previously committed contents of deploy_branch 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 $deploy_directory. Skipping commit.;;
	1)
		set_user_id
		git --work-tree "$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 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
		exit $diff
		;;
esac

restore_head