I generally use NMAP for any type of host discovery, but recently started experimenting with FPing. One thing I found is that, when performing a ping sweep, not only do I see the hosts that replied to the ping, but FPing also sends any unreachable IP addresses to stdout (which is super annoying and ugly if you ask me...).
Anyway, after a bit of research, I found a nifty way to suppress these messages. Linux allows us to redirect all error messages to /dev/null. So instead of just running the vanilla fping -a -g.... you would run the program and output all error messages /dev/null, like so: