isInstalled() {
  if [ "$(which $1)" != "" ]; then
    return 0
  fi
  return 1
}

installOptional() {
  echo "install optional '$*'"

  # Check if any of the listed programs are installed
  # if not install the first one;
  for prog in "$@"; do
    if isInstalled $prog; then
      echo "$prog is installed"
      break
    fi
  done

  install $1

}

install() {
  # Check if program is already installed
  if isInstalled $1; then
    echo " ✓ $1 is already installed"
  else
    echo " - installing $1 ..."
    apt-get install $1 -y >/dev/null
    echo " ✓ finished"
  fi
}

[[ "${1}" != "--source-only" ]] && install "${@}"