function gch() {
	local currentBranch=$(git rev-parse --abbrev-ref HEAD)
	local previousFile="$(git rev-parse --show-toplevel)/.git/PREVIOUS_HEAD"
	if [ -n "$1" ]; then
		echo "$currentBranch" >> $previousFile
		git checkout "$@"
	else
		if [ ! -f "$previousFile" ]; then echo >&2 "ERROR: Missing PREVIOUS_HEAD. Please run gch with 1 argument first."
		else
			git checkout "$(cat $previousFile | tail --lines=1)"
			echo "$currentBranch" >> $previousFile
		fi
	fi
	# truncate the file
	tail -n10 $previousFile > "$previousFile.TEMP"
	mv -f "$previousFile"{.TEMP,}
}