[damir]

This is how i do it on my Mac. Open the terminal:

nano -w .profile

and than paste following:

alias myip='curl -s http://www.whatismyip.com/automation/n09230945.asp | grep -o '[0-9][0-9]*.[0-9][0-9]*.[0-9][0-9]*.[0-9]*''

Save and quit the file. Afte that just type myip and you will get you external IP.