gethostbyaddr

gethostbyaddr 
address
, [
addrtype
]

Retrieves the hostname (and alternate addresses) of a packed binary network address . ( addrtype indicates the type of address given. Since gethostbyaddr is used almost solely for Internet IP addresses, addrtype is not needed.) The return value in list context is:

($name, $aliases, $addrtype, $length, @addrs)

where @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[0]);

In scalar context, gethostbyaddr returns only the hostname.