system command?

Anyone know what this wouldn't work? I have tried using a couple of functions defined at http://us2.php.net/manual/en/ref.exec.php and none seem to have the desired effect. <?php $tailed = shell_exec('tail -f /path/to/log'); //$tailed = exec('tail -f /path/to/log'); //$tailed = system('tail -f /path/to/log'); print = "<textarea>$tailed</textarea>"; ?> Thanks in advance, Jas