http://scottlee.me/use-dropbox-to-track-external-ip-address/

connect_to_home.sh

#!/bin/bash  

# Get IP address from output file in Dropbox. 
ip=`cat ~/Dropbox/HomeNetworkIP.txt`  

# Establish SSH session
ssh $ip

# To connect:
# ./Dropbox/scripts/connect_to_home.sh

getexternalip.sh

#!/bin/bash 

# Specify output file for IP address here.
ip_file=HomeNetworkIP.txt

# --------------------------- #
# Let's get down to business
# --------------------------- #

# Get current IP address
current_ip=$(curl -s http://icanhazip.com)  

# If the IP file exist, grab the old IP address
if [ -f "$ip_file" ] 
then 
	old_ip=$(<$ip_file)
fi 

# If current IP address is NOT the same as the old update the IP file.
if [ $current_ip != $old_ip ]
then
	echo $current_ip > $ip_file 
else 
	exit
fi