Simple bash function for checking if new usb serial converter has been attached. Tested on Ubuntu 18.04. Use PATH_NAME=$(wait_for_new_usb_serial)

fw.sh

function wait_for_new_usb_serial() {

        local array=(`ls -1 //sys/bus/usb-serial/devices/`)
        local ret=""
        local   current_devices

        while (true) do
        sleep 2
        current_devices=(`ls -1 //sys/bus/usb-serial/devices/`)
        for  value in "${current_devices[@]}" 
        do
        if [[ ! " ${array[@]} " =~ " ${value} " ]]; then
                echo "$value"
                ret="x"
                break
        fi
        done
        if [[ ! "x$ret" = "x" ]]; then
                break
        fi
        array=("${current_devices[@]}")
        done
        
}