[TheDong]

"matches an ip address" is a vague enough specification that of course people fail.

Is it what `inet_addr` accept? In that case, "1", "0x1", "00.01", "00000.01", and more are all ip addresses. `ping` accepts all of em anyway.

Is a valid ipv6 address one with the square brackets around it? Is "::1" a valid ip address? What about "fe80::1%eth2"? ping accepts both of these on my machine (though probably not on yours, since you probably don't have an eth2 interface)

[NikkiA]

square brackets around an IP address predates IPv6, it was/is? used to bypass DNS lookups and some (very) old programs required IP addresses inside [...] otherwise they were assumed to be a domain name with all the rules that implied.