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

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

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

NNAAMMEE #

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

SSYYNNOOPPSSIISS #

  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;

DDEESSCCRRIIPPTTIIOONN #

 This module's default exports override the core ggeettnneettbbyynnaammee(()) and
 ggeettnneettbbyyaaddddrr(()) 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 _n_e_t_d_b_._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 ggeettnneett(()) function is a simple front-end that forwards a numeric
 argument to ggeettnneettbbyyaaddddrr(()), and the rest to ggeettnneettbbyynnaammee(()).

 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.

EEXXAAMMPPLLEESS #

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

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

 The ggeetthhoosstt(()) 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;
         }
      }
  }

NNOOTTEE #

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

AAUUTTHHOORR #

 Tom Christiansen

perl v5.36.3 2019-02-13 Net::netent(3p)