读取ifconfig数据实时显示保存

#!/bin/bash
ethn=$1

while true
do
  RX_pre=$(cat /proc/net/dev | grep $ethn | sed 's/:/ /g' | awk '{print $2}')
  TX_pre=$(cat /proc/net/dev | grep $ethn | sed 's/:/ /g' | awk '{print $9}')
  sleep 1
  RX_next=$(cat /proc/net/dev | grep $ethn | sed 's/:/ /g' | awk '{print $2}')
  TX_next=$(cat /proc/net/dev | grep $ethn | sed 's/:/ /g' | awk '{print $9}')

  clear
  echo -e "`date +%k:%M:%S` RX            TX"
  #echo "${RX_next} ${RX_pre} \t ${TX_next} ${TX_pre}"
  RX=$((${RX_next}-${RX_pre}))
  TX=$((${TX_next}-${TX_pre}))

if [[ $RX -ne 0 ]]; then
  if [[ $RX -lt 1024 ]];then
    #RX="${RX}B/s"
    RX=$(echo $RX | awk '{print $1*8 "bps"}')
  elif [[ $RX -gt 1048576 ]];then
    #RX=$(echo $RX | awk '{print $1/1048576 "MB/s"}')
    RX=$(echo $RX | awk '{print $1/131072 "Mbps"}')
  else
    #RX=$(echo $RX | awk '{print $1/1024 "KB/s"}')
    RX=$(echo $RX | awk '{print $1/128 "Kbps"}')
  fi
fi
if [[ $TX -ne 0 ]]; then
  if [[ $TX -lt 1024 ]];then
    #TX="${TX}B/s"
     TX=$(echo $TX | awk '{print $1*8 "bps"}')
  elif [[ $TX -gt 1048576 ]];then
    #TX=$(echo $TX | awk '{print $1/1048576 "MB/s"}')
    TX=$(echo $TX | awk '{print $1/131072 "Mbps"}')
  else
    #TX=$(echo $TX | awk '{print $1/1024 "KB/s"}')
    TX=$(echo $TX | awk '{print $1/128 "Kbps"}')
  fi
fi
  echo -e "$ethn \t $RX   $TX "
  echo "`date +%Y-%m-%d,%k:%M:%S` $ethn  RX:$RX  TX:$TX ">> /opt/net.log
done