shuffle string

<?php

function shuffle($str) {
  $shuffled = "";
  $l = strlen($str);
  for ($i = 0; $i < $l; $i++) {
    $ch = substr($str, $i, 1);
    if ($ch == ' ')
      continue;
    $shuffled .= $ch;
  }
  $shuffled = str_shuffle($shuffled);
  $i = 0;
  $shuffled_str = '';
  for ($j = 0; $j < $l; $j++) {
    $ch = substr($str, $j, 1);
    if ($ch == ' ')
      $shuffled_str .= ' ';
    else
      $shuffled_str .= $shuffled[$i++];
  }
  return $shuffled_str;
}

echo shuffle("This is a test");

?>