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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

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

       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

perl v5.8.8                       2001-09-21                    Net::netent(3)