This function does the same thing as
gethostbyaddr(3): it translates
a packed binary network address to its corresponding
names (and alternate addresses).
The return value in list context is:
($name, $aliases, $addrtype, $length, @addrs)
is a list of packed binary addresses. In the Internet domain, each address is
four bytes long, and can be unpacked by saying something like:
($a, $b, $c, $d) = unpack('C4', $addrs);
In scalar context, gethostbyaddr returns only the host name.
See the section on "Sockets" in Chapter 6 for another approach.