Net::netent(3)         Perl Programmers Reference Guide         Net::netent(3)

       Net::netent - by-name interface to Perl's built-in getnet*() functions

        use Net::netent qw(:FIELDS);
        getnetbyname("loopback")               or die "bad net";
        printf "%s is %08X\n", $n_name, $n_net;

        use Net::netent;

        $n = getnetbyname("loopback")          or die "bad net";
        { # there's gotta be a better way, eh?
            @bytes = unpack("C4", pack("N", $n->net));
            shift @bytes while @bytes && $bytes[0] == 0;
        printf "%s is %08X [%d.%d.%d.%d]\n", $n->name, $n->net, @bytes;

       This module's default exports override the core getnetbyname() and
       getnetbyaddr() functions, replacing them with versions that return
       "Net::netent" objects.  This object has methods that return the
       similarly named structure field name from the C's netent structure from
       netdb.h; namely name, aliases, addrtype, and net.  The aliases method
       returns an array reference, the rest scalars.

       You may also import all the structure fields directly into your
       namespace as regular variables using the :FIELDS import tag.  (Note
       that this still overrides your core functions.)  Access these fields as
       variables named with a preceding n_.  Thus, $net_obj->name()
       corresponds to $n_name if you import the fields.  Array references are
       available as regular array variables, so for example @{
       $net_obj->aliases() } would be simply @n_aliases.

       The getnet() funtion is a simple front-end that forwards a numeric
       argument to getnetbyaddr(), and the rest to getnetbyname().

       To access this functionality without the core overrides, pass the use
       an empty import list, and then access function functions with their
       full qualified names.  On the other hand, the built-ins are still
       available via the CORE:: pseudo-package.

       The getnet() functions do this in the Perl core:

           sv_setiv(sv, (I32)nent->n_net);

       The gethost() functions do this in the Perl core:

           sv_setpvn(sv, hent->h_addr, len);

       That means that the address comes back in binary for the host
       functions, and as a regular perl integer for the net ones.  This seems
       a bug, but here's how to deal with it:

        use strict;
        use Socket;
        use Net::netent;

        @ARGV = ('loopback') unless @ARGV;

        my($n, $net);

        for $net ( @ARGV ) {

            unless ($n = getnetbyname($net)) {
               warn "$0: no such net: $net\n";

            printf "\n%s is %s%s\n",
                   lc($n->name) eq lc($net) ? "" : "*really* ",

            print "\taliases are ", join(", ", @{$n->aliases}), "\n"
                       if @{$n->aliases};

            # this is stupid; first, why is this not in binary?
            # second, why am i going through these convolutions
            # to make it looks right
               my @a = unpack("C4", pack("N", $n->net));
               shift @a while @a && $a[0] == 0;
               printf "\taddr is %s [%d.%d.%d.%d]\n", $n->net, @a;

            if ($n = getnetbyaddr($n->net)) {
               if (lc($n->name) ne lc($net)) {
                   printf "\tThat addr reverses to net %s!\n", $n->name;
                   $net = $n->name;

       While this class is currently implemented using the Class::Struct
       module to build a struct-like class, you shouldn't rely upon this.

       Tom Christiansen

3rd Berkeley Distribution    perl 5.005, patch 02               Net::netent(3)