use warnings;

$logfile="log.txt";
$error="DOWN";
$warn="PROBLEM";
$redbutton="\<img src\=\'default_files/perlredblink2\.gif'>";
$greenbutton="\<img src\=\'default_files/perlgreenblink\.gif'>";
$yellowbutton="\<img src\=\'default_files/perlyellowblink\.gif'>";

open LOG, $logfile or die "Cannot open $logfile for read :$!";

my $button = $greenbutton;

while (<LOG>) {
if ($_ =~ /$error/i) {
  $button = $redbutton;
  print "<!--Content-type: text/html-->\n\n";
     print "$redbutton";
  }
if ($_ =~ /$warn/i) {
  $button = $yellowbutton;
  print "<!--Content-type: text/html-->\n\n";
     print "$yellowbutton";
  }
}
close LOG;