SCREEN_SESSION="server"


check_session () {
    screen -S "${SCREEN_SESSION}" -Q select . >/dev/null
    return $?
}

start_session () {
    check_session && {
        echo "Server is already running!"
        return 1
    }
    screen -dmS "${SCREEN_SESSION}" "echo 5"
}

attach_session () {
    check_session || {
        echo "Session is not running!"
        return 1
    }
    screen -S "${SCREEN_SESSION}" -x
}

if ! check_session; then
  start_session
else
  attach_session
fi