I trie to get the result code of exec, system or passthru function but i always get -1 under linux. version of php: 4.0.3pl1 et 4.0.4pl1

<?
passthru("/bin/echo test",$r);
echo $r;

system("/bin/echo test", $r);
echo $r;

?>

I trie under winnt 4 sp6/apache 1.3.14 and it's works fine 
<? 
passthru("echo test", $r;
echo $r;
?>