linux查看每秒的网络流量

import os
import time
cmd = ‘ifconfig  | grep "RX bytes" | head -1 | awk -F":" \‘{print $2," ", $3}\‘ | awk \‘{print $1 , " " , $6}\‘ > network_speed.temp‘
os.system(cmd)
tx=0
rx=0
while True:
    file = open(‘network_speed.temp‘)
    for line in file:
        fields = line.strip().split()
        print (int(fields[0]) - tx)/1024.0/1024.0, " ", (int(fields[1]) - rx)/1024.0/1024.0
        tx = int(fields[0])
        rx= int(fields[1])
    time.sleep(1)
    os.system(cmd)