How to random array?

[achoo254]

It's not working.

Code:

<?php
$display = 'hello word - hello word - hello word';
$find = 'h'; 
$replace = array('1','2','3','4');
$output = str_replace(array_fill(0, count($replace), $find), $replace, $display);
echo $output;
?>

Display:

1ello word - 1ello word - 1ello word