extracting an IPv4 address from text?

Hello:
	Let's suppose I want to parse a line from auth.log and extract
the IP address (if any) to stdout.
	I'm assuming there is a robust way to do this using standard
command-line tools ... but my brain is flailing on the exact method.
Anyone have a example they'd be willing to share?  Or is this a
problem already solved?


				Hopefully,


					Robert Huff