LINUX에서 특정 eth에서 주고받는 패킷의 갯수를 셀수 있는 방법이 무엇인가요?

#!/bin/bash 
 
# Packet Data Count하는 가장 쉬운 방법은? ^ㅡ^
# Scripted by WONTOP
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echo "====================================================================" 
echo " 해당 쉘 스크립트는 주고 받는 패킷의 "
echo " SIZE or COUNT를 숫자로 표시하도록 구현되어있습니다." 
echo " 일단 Trace하고 싶은 Ethernet Card 번호를 입력하세요" 
echo "====================================================================" 
 
echo -n " #### Ethernet Card Num : "
read ETH_NUM
 
echo -n " #### PACKET SIZE(1) or PACKET COUNT(2) : "
read FLAG
 
echo -n " #### Sleep Time : "
read SLEEP_TIME 
 
 
if [ "1" == "$FLAG" ];
then
 
    TX_FIRST_DATA_SIZE=$(cat /sys/class/net/eth$ETH_NUM/statistics/tx_bytes)
    RX_FIRST_DATA_SIZE=$(cat /sys/class/net/eth$ETH_NUM/statistics/rx_bytes)
 
    while [ 1 ];
    do
        echo ""
        date
        echo -n  "tx size : "
        TEMP=$(cat /sys/class/net/eth$ETH_NUM/statistics/tx_bytes)
        TEMP=$(($TEMP-TX_FIRST_DATA_SIZE))
        echo $TEMP
        echo -n  "rx size : "
        TEMP=$(cat /sys/class/net/eth$ETH_NUM/statistics/rx_bytes)
        TEMP=$(($TEMP-RX_FIRST_DATA_SIZE))
        echo $TEMP
        sleep $SLEEP_TIME;
    done
 
elif [ "2" == "$FLAG" ]; 
then
 
    TX_FIRST_DATA_COUNT=$(cat /sys/class/net/eth$ETH_NUM/statistics/tx_packets)
    RX_FIRST_DATA_COUNT=$(cat /sys/class/net/eth$ETH_NUM/statistics/rx_packets)
 
    while [ 1 ];
    do
        echo ""
        date
        echo -n  "tx count : "
        TEMP=$(cat /sys/class/net/eth$ETH_NUM/statistics/tx_packets)
        TEMP=$(($TEMP-TX_FIRST_DATA_COUNT))
        echo $TEMP
        echo -n  "rx count : "
        TEMP=$(cat /sys/class/net/eth$ETH_NUM/statistics/rx_packets)
        TEMP=$(($TEMP-RX_FIRST_DATA_COUNT))
        echo $TEMP
        sleep $SLEEP_TIME;
    done
 
else
    echo "잘못 선택 하셨습니다"
fi