#!/usr/bin/perl -w

use strict;

my $user;
my $tty;
my $count;
my @where;
my %count = ();
my %where = ();


foreach $_ (`who`) {
       ($user,$tty) = /(\S+)\s+(\S+)/;
       $count{$user}++;
       $where{$user}{$tty}++;
}

foreach (sort keys %count) {
      if ($count{$_} == 1) {
                print "user $_ is ONLY logged in at one place ";
                print $where->{$_};
      } else {
                print "user $_ is logged in at: ";
                @where = sort keys %{$where{$_}};
                print "@where\n";
      }
}
~