#!/bin/bash
gateway=$(ip route show 0.0.0.0/0 | awk '{print $3}')
mactest=$(arp -n -a $gateway | awk '{print $4}')
targetmac="XX:XX:XX:XX:XX:XX"
homeup="mount -t cifs -o username=USER,password=PASSWORD //SERVER/SHARE /mnt/remote"
awayup="sshfs my.dyndns.tld:/path/to/share /mnt/remote"
down="umount -l /mnt/remote"
if [ $mactest==$targetmac ]
then
	case "$2" in
        	up)
               		$homeup
        	;;
        	down)
               		$down
        	;;
	esac
else
	case "$2" in
		up)
			$awayup
		;;
		down)
			$down
		;;
	esac
fi

exit $?

#!/bin/bash
gateway=$(ip route show 0.0.0.0/0 | awk '{print $3}')
mactest=$(arp -n -a $gateway | awk '{print $4}')
targetmac="XX:XX:XX:XX:XX:XX"
homeup="mount -t cifs -o username=USER,password=PASSWORD //SERVER/SHARE /mnt/remote"
awayup="sshfs my.dyndns.tld:/path/to/share /mnt/remote"
down="umount /mnt/remote"
if [ $mactest==$targetmac ]
then
	case "$2" in
        	up)
               		$homeup
        	;;
        	down)
               		$down
        	;;
	esac
else
	case "$2" in
		up)
			$awayup
		;;
		down)
			$down
		;;
	esac
fi

exit $?

#!/bin/bash
gateway=`ip route show 0.0.0.0/0 | awk '{print $3}'`
mactest=$(arp -n -a $gateway | awk '{print $4}')
targetmac="00:00:00:00:00:00"
upcommand="mount /media/net"
downcommand="umount /media/net"
if [ $mactest==$targetmac ]
then
	case "$2" in
        	up)
               		$upcommand
        	;;
        	down)
               		$downcommand
        	;;
	esac

fi
exit $?

http://nathanewilliams.com/

updated...

Network Event Triggered Bash Script

event, Bash, script

Bash