This is the normal version and just displays up or down in plain tekst.
<?php
$return_var = exec('pidof $app_name');
  if ($return_var>0) {
      echo "Up";
      }
  if ($return_var==0) {
      echo "DOWN";
      }
?>



Fancy version
<?php
$return_var = exec('pidof $app_name');
  if ($return_var>0) {
      echo "<b><font color=blue>Up</font></b>";
      }
  if ($return_var==0) {
      echo "<b><font color=red>DOWN</font></b>";
      }
?>


Fancy version with pid showing when the app is up
<?php
$return_var = exec('pidof $app_name');
  if ($return_var>0) {
      echo "<b><font color=blue>Up</font></b>, with pid: ";
      echo $return_var;
      }
  if ($return_var==0) {
      echo "<b><font color=red>DOWN</font></b>";
      }
?>