If all you want to do is enable file sharing, shares are already setup, it's fairly simple:

launchctl load -w /System/Library/LaunchDaemons/com.apple.AppleFileServer.plist

If you need to also setup the share points, take a look at the following page. It's fairly old, but it all appears to still apply.
http://systemsboy.com/2008/03/netboot-part-4.html

NIce!

I was looking for the GUI visual, but the file sharing checkbox doesn't check unless you reboot.
loading and unloading will turn on and off on the fly.

Thanks Josh

Dan