Get all MAC addresses in default network

find_all_macs.sh

#!/usr/bin/env bash

#getting the default interface and ping the broadcast address to get all network IPs
if [ "$(uname)" == "Darwin" ]; then
    interface=$(route -n get default | grep 'interface:' | grep -o '[^ ]*$') 
    broadcast=$(ifconfig | grep -A 2 $interface | tail -n 1 | cut -d\  -f6)
    ping -c 4  -W 2000 $broadcast    
elif [ "$(expr substr $(uname -s) 1 5)" == "Linux" ]; then
    interface=$(route | grep '^default' | grep -o '[^ ]*$')
    broadcast=$(/sbin/ifconfig $interface | grep 'inet addr' | cut -d: -f3 | awk '{print $1}')
    ping -c 4  -W 2 -b $broadcast
fi

arp -a | cut -d\  -f4