Output the difference between data in script

Question

I have tried to make script which can help me to output info about received and transmitted data on specific interface. Here is the beginning stuff of it:

#!/bin/bash

interface=$1

while true; do
ip -s link ls $interface | awk '{ print $1 "\t" $2}'

sleep 10
done

But also I want to get the difference of changes in data. I haven't the faintest idea how to output it. So for i.e. I get this from my script line ip -s link ls $interface | awk '{ print $1 "\t" $2}':

2:      enp0s3:
link/ether      08:00:27:ad:a6:53
RX:     bytes
38134   399
TX:     bytes
34722   247

I want to get the difference between 38134 and 34722 and then the difference between 399 and 247 and add to some file for example.

Answer 1

I have an ugly script that can answer your needs. The idea is:

• store interface stats in a file
• read the file line by line
• if line containts RX (resp TX), that means that the following line contains information you want to parse.

The script:

#!/bin/bash

ip -s link ls $interface > ip_stats

RX=0
TX=0
# read file
while read LINE
do 
    # read RX info form line
    if [ $RX -eq 1 ]
    then
        RX_packets=$(echo $LINE | awk '{print $1}')
        RX_bytes=$(echo $LINE | awk '{print $2}')        
    fi
    # see if next line will contain RX stats
    if echo $LINE | grep RX 
    then
        RX=1
    else
        RX=0
    fi

    # read TX info form line
    if [ $TX -eq 1 ]
    then
        TX_packets=$(echo $LINE | awk '{print $1}')
        TX_bytes=$(echo $LINE | awk '{print $2}')        
    fi
    # see if next line will contain TX stats
    if echo $LINE | grep TX 
    then
        TX=1
    else
        TX=0
    fi

done < ip_stats

echo RX_packets is $RX_packets
echo TX_packets is $TX_packets

echo RX_bytes is $RX_bytes
echo TX_bytes is $TX_bytes

# make diff
echo packets diff: $(expr $RX_packets - $TX_packets )
echo bytes diff: $(expr $RX_bytes - $TX_bytes )