#!/usr/bin/perl -l -w0777

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

while(sleep 2) {
  $_ = `users`;
  for my $n (keys %users) {
    if ($users{$n} xor /\b$n\b/) {
      $users{$n} = /\b$n\b/;
      print localtime() . " $n has logged ", $users{$n} ? "in" : "out";
    }
  }
}