#!/bin/bash
export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

NIC=$1
echo -e "Time ----------------- In ------- Out"
while true; do
    OLD_IN=$(awk '/'$NIC'/ {print $2}' /proc/net/dev)
    OLD_OUT=$(awk '/'$NIC'/ {print $10}' /proc/net/dev)
    sleep 1
    NEW_IN=$(awk '/'$NIC'/ {print $2}' /proc/net/dev)
    NEW_OUT=$(awk '/'$NIC'/ {print $10}' /proc/net/dev)
    IN=$(printf "%.1f%s" "$((($NEW_IN-$OLD_IN)/1024))" "KB/s")
    OUT=$(printf "%.1f%s" "$((($NEW_OUT-$OLD_OUT)/1024))" "KB/s")
    echo "$(date "+%Y-%m-%d %H:%M:%S")    $IN    $OUT"
done