#!/bin/bash
function open_tty()
 {
 if [ -e "/dev/ttyUSB0" ]; then
    SERIAL="ttyUSB0"
 elif [ -e "/dev/ttyUSB1" ]; then
    SERIAL="ttyUSB1"
 elif [ -e "/dev/ttyUSB2" ]; then
    SERIAL="ttyUSB2"
 elif [ -e "/dev/ttyUSB3" ]; then
    SERIAL="ttyUSB3"
 fi
 if [ -z "$SERIAL" ]; then
    echo "No USB-to-SERIAL detected"
 else
    screen /dev/$SERIAL
 fi
 }
if [ `id -un` != "root" ]; then
   echo "Enter root password to open tty:"
   su -c "serialread"
   exit 0
else
   open_tty
fi