Basta Colocar o script abaixo para ficar rodando no crontab.
#!/bin/bash
PATH=$PATH:$HOME/bin
PATH=$PATH:/sbin:/usr/sbin
export PATH
FILE=”/etc/scripts/firewall/mac.txt”
achou=”0″
for macfor in `/sbin/arp -n | /bin/grep ether | /bin/grep C | /bin/grep ‘192.168.10’ | /bin/awk ‘{print $3 $4 $1}’`
do
for macregistrados in `/bin/cat $FILE | /bin/cut -d “=” -f 1`
do
MAC=${macfor:0:17}
IP=${macfor:18:15}
if [ “$macregistrados” == “$MAC” ]
then
achou=”1″
fi
done
if [ “$achou” == “0” ]
then
MAC=${macfor:0:17}
IP=${macfor:18:15}
echo $MAC”=”$IP” Achei”
echo $MAC”=”$IP”=A=NOVO______” >> $FILE
fi
achou=”0″
done