Sys::Hostname::FQDN uses the host 'C' library
to discover the (usually) short host name,
then uses (perl) gethostbyname to extract the real hostname.

The results from gethostbyname are exported as gethostinfo
and asciihostinfo as a convenience since they are available.
Similarly, the 'C' library functions inet_ntoa and inet_aton are exported.

WWW: https://metacpan.org/release/Sys-Hostname-FQDN