MAN page from Old RedHat 5.X perl-5.004-4.i386.rpm

Net::netent

Section: Perl Programmers Reference Guide (3)
Updated: perl 5.004, patch 04
Index

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() andgetnetbyaddr() functions, replacing them with versions that return``Net::netent'' objects. This object has methods that return the similarlynamed 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 namespaceas regular variables using the :FIELDS import tag. (Note that this stilloverrides your core functions.) Access these fields as variables namedwith a preceding n_. Thus, $net_obj->name() corresponds to$n_name if you import the fields. Array references are available asregular array variables, so for example @{ $net_obj->aliases()} would be simply @n_aliases.

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

To access this functionality without the core overrides,pass the use an empty import list, and then accessfunction functions with their full qualified names.On the other hand, the built-ins are still availablevia 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 thehost 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::Structmodule to build a struct-like class, you shouldn't rely upon this.

AUTHOR

Tom Christiansen

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