Provided by: perl-doc_5.26.1-6_all bug


       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() function 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