实现代码：

#!/bin/bash

eth_in_old=$(ifconfig eth0|grep "RX bytes"|sed 's/RX bytes://'|awk '{print $1}')
eth_out_old=$(ifconfig eth0|grep "RX bytes"|sed 's/.*TX bytes://'|awk '{print $1}')

sleep 1

eth_in_new=$(ifconfig eth0|grep "RX bytes"|sed 's/RX bytes://'|awk '{print $1}')
eth_out_new=$(ifconfig eth0|grep "RX bytes"|sed 's/.*TX bytes://'|awk '{print $1}')
eth_in=$(echo "scale=2;($eth_in_new - $eth_in_old)/1000.0"|bc)
eth_out=$(echo "scale=2;($eth_out_new - $eth_out_old)/1000" | bc)
echo "IN: $eth_in KB"
echo "OUT:$eth_out KB"

输出：
[root@localhost hbshell]# ./traffic.sh

IN: 1.74 KB
OUT:1.17 KB