#!/usr/bin/perl -w0777

@users{split /\s+/, <DATA>}=();

while(sleep 2) {
  for my $n (keys %users) {
    $_ = `users`;
    $state = '';
    $users{$n} = 1, $state = 'in'  if !$users{$n} &&  /\b$n\b/;
    $users{$n} = 0, $state = 'out' if  $users{$n} && !/\b$n\b/;
    print localtime() . " $n has logged $state\n" if $state;
  }
}