http://blog.chinaunix.net/u/22677/showart_2115362.html

ifconfig，会有这样的输出： RX bytes:1224128649 (1.1 GiB)  TX bytes:34114947 (32.5 MiB)

过一会再看，数值有所变化，两者的差值就是过去一段时间的流量。可是，这也太不人性化了……

正所谓自己动手，丰衣足食，我们自己来写一个脚本，实时显示并刷新！

脚本如下，还是哪句话，本人功力有限，写脚本的原则是够用就好。

#!/bin/bash

if [ -n "$1" ]; then
  eth_name=$1
else
  eth_name="eth0"
fi

i=0

send_o=`ifconfig $eth_name | grep bytes | awk '{print $6}' | awk -F : '{print $2}'`
recv_o=`ifconfig $eth_name | grep bytes | awk '{print $2}' | awk -F : '{print $2}'`
send_n=$send_o
recv_n=$recv_o

while [ $i -le 100000 ]; do
  send_l=$send_n
  recv_l=$recv_n
  sleep 1
  send_n=`ifconfig $eth_name | grep bytes | awk '{print $6}' | awk -F : '{print $2}'`
  recv_n=`ifconfig $eth_name | grep bytes | awk '{print $2}' | awk -F : '{print $2}'`
  i=`expr $i + 1`
  send_r=`expr $send_n - $send_l`
  recv_r=`expr $recv_n - $recv_l`
  total_r=`expr $send_r + $recv_r`
  send_ra=`expr /( $send_n - $send_o /) / $i`
  recv_ra=`expr /( $recv_n - $recv_o /) / $i`
  total_ra=`expr $send_ra + $recv_ra`
  sendn=`ifconfig $eth_name | grep bytes | awk -F /( '{print $3}' | awk -F /) '{print $1}'`
  recvn=`ifconfig $eth_name | grep bytes | awk -F /( '{print $2}' | awk -F /) '{print $1}'`
  clear
  echo  "Last second  :   Send rate: $send_r Bytes/sec  Recv rate: $recv_r Bytes/sec  Total rate: $total_r Bytes/sec"
  echo  "Average value:   Send rate: $send_ra Bytes/sec  Recv rate: $recv_ra Bytes/sec  Total rate: $total_ra Bytes/sec"
  echo  "Total traffic after startup:    Send traffic: $sendn  Recv traffic: $recvn"
done

该脚本（假设名叫traffic）默认显示eth0的流量，如果你有多个网卡，请将网卡作为参数传进去，比如：
./traffic  eth1

运行结果如下：