monitor network traffic

#!/bin/bash

while true
do
    # replace wlp0s20f3 with your network interface
    # replace 7 and 5 with your output of ifconfig, this command get RX and TX bytes of ifconfig
    RX_pre=`ifconfig wlp0s20f3 | awk 'NR==7{print $5}'`
    TX_pre=`ifconfig wlp0s20f3 | awk 'NR==9{print $5}'`
    sleep 1
    RX_aft=`ifconfig wlp0s20f3 | awk 'NR==7{print $5}'`
    TX_aft=`ifconfig wlp0s20f3 | awk 'NR==9{print $5}'`

    clear
    echo -e "`date +%k:%M:%S` \t TX \t RX"

    RX=$((RX_aft-RX_pre))
    TX=$((TX_aft-TX_pre))

    echo -e "\t \t $TX \t $RX "

    if [ $RX -lt 1024 ];then
        echo "${RX}k/s"
        elif [ $RX -lt 1048576 ];then
        echo "$((RX/1024))kb/s"
    else
        echo "$((RX/1048576))m/s"
    fi
    if [ $TX -lt 1024 ];then
        echo "${TX}k/S"
        elif [ $TX -lt 1048576 ];then
        echo "$((TX/1024))kb/s"
    else
        echo "$((TX/1048576))m/s"
    fi
done