getnets -4 ASN or getnets --ipv4 ASN - same as first
getnets -6 ASN or getnets --ipv6 ASN - for IPv6 subnets
getnets -h|--help for help
bash 4.3.042
whois 5.2.7
sed 4.2.2
coreutils 8.24
Specified version is one that I use while write this script, I think it
can work on any version of this utilities (but may be not).
This little bash script help you found all ISP IPv4 (or v6) networks (inetnums).
It can do so by search in RADB database and output one at a string.
NOTE It can print network which can be sub(super)nets for already
printed network.