Article 6972 of comp.lang.perl:
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From: max@cis.uni-muenchen.de (Max Hadersbeck)
Subject: Develop DISPLAY Variable for X at login time.
Message-ID: <CF53qL.KDy@informatik.uni-muenchen.de>
Sender: max@user@cis.uni-muenchen.de (Max Hadersbeck)
Date: Tue, 19 Oct 1993 10:27:56 GMT
Reply-To: max@cis.uni-muenchen.de
Organization: CIS, University of Munich
X-Newsreader: mxrn 6.18-4
Keywords: DISPLAY Variable X- Windows
Lines: 81


Hi
Here is a program, which I find very useful in a login procedure.
If you log into a machine you must set your display variable to your
host and screen. The output of who truncates your machinename. So
use this script.
MAX
---------------------------------
cut here :

#!/bin/perl
# title : getXdisplayvar.pl
# author :
#----------------------------------------------------------------------
#Maximilian Hadersbeck     | Wagmuellerstr. 23  | Phone: +49 89 2110672
#CIS                       | D-80538 M"unchen   | Fax:   +49 89 2110674
#University of Munich      | Germany            | max@cis.uni-muenchen.de
#----------------------------------------------------------------------
# Version : 1.0
# This program gets the right host and display-name for your DISPLAY
# variable. This is very usefull in a login script, 
# if you connect to a remote machine
#

# get user name and terminal number :
$iam=`whoami`;
chop $iam;
$termid=`tty`;
$termid=~ s/\/dev\///;
chop $termid;

# get hostname extract
open(WHOFILE,"who |");
while (<WHOFILE>)

{
 ($name,$term,$mon,$day,$time,$host_split) = split(' ',$_);
  if ( length $host_split && $name eq $iam && $term eq $termid)
	{
	$host = $host_split;
	last;
	};
};
close (WHOFILE);


if ( $host =~ /\./ )
{
 if   ( ! $host =~ /0/)
   { 
	($hostx,$rest) = split(/\./,$host,2);
	 chop $hostx;
   	 $hostx =~ s/\(//; 
   };
 if ($host =~ /0/)
   {
	$hostx = `hostname`;
	chop $hostx;
    };
}
else
{
  $hostx = $host;
  $hostx =~ s/^\((.*)\)$/$1/;
};

print "You come from the host  : $hostx \n";

$host_from = &name_to_address($hostx);

print "Your IP-number and display is  $host_from:0.0\n";


sub name_to_address {
   local ($name) = shift (@_);
   local (@octets);
   local ($nam, $aliases, $addrtype, $length, $address) = gethostbyname ($name);
   if (! length ($address)) { die "$prog: no address found for $name\n"; }
   @octets = unpack ("CCCC", $address);
   join ('.', @octets[0..3]);
}