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



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

SYNOPSIS
        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;

DESCRIPTION
       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.

EXAMPLES
       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";
               next;
            }

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

            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;
                   redo;
               }
            }
        }

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

AUTHOR
       Tom Christiansen



perl v5.16.2                                     2012-08-26                                 Net::netent(3pm)