Snort Box IP assigned by DHCP

["Palula Brasil" <palula () uol com br>]

Hi there!

Here is the problem. Every time I turn on the box, I have to look at the IP assigned by the ISP, edit snort.conf and, 
in the HOME_NET variable, I put the DHCP assigned address manually and after that, I start Snort and it works fine.

What I'd like to know is: Is there a way for me to automatically have snort to know what IP has been assigned and work 
with that IP. I've used both of these variables and it didn't work:

var HOME_NET $eth0_ADDRESS
and
var HOME_NET $eth0

But still... None worked.

Does Linux need some kind of program to make global variables work?