#!/bin/bash

files=(/sys/class/net/*)
pos=$(( ${#files[*]} - 1 ))
last=${files[$pos]}

json_output="{"

for interface in "${files[@]}" 
do
	basename=$(basename "$interface")
	
	# find the number of bytes transfered for this interface
	in1=$(cat /sys/class/net/"$basename"/statistics/rx_bytes)

	# wait a second
	sleep 1

	# check same interface again
	in2=$(cat /sys/class/net/"$basename"/statistics/rx_bytes)

	# get the difference (transfer rate)
	in_bytes=$((in2 - in1))

	# convert transfer rate to KB
	in_kbytes=$((in_bytes / 1024))

	# convert transfer rate to KB
	json_output="$json_output \"$basename\": $in_kbytes"

	# if it is not the last line
	if [[ ! $interface == $last ]]
	then
		# add a comma to the line (JSON formatting)
		json_output="$json_output,"
	fi 
done

# close the JSON object & print to screen
echo "$json_output}"