default_os=ubuntu
default_os_codename=bionic

os=${1:-$default_os}
os_codename=${2:-$default_os_codename}
build_tag="${3:-}"
if [[ -n "$build_tag" ]]; then
   build_tag_for_images="_${build_tag#+}"
   build_debian_revision="$(echo $build_tag | tr _ -)"
fi
os_image="$os:$os_codename"

echo "Building for $os_image"