Print all permutations of a string

permute("123", 0, 3);

function permute($str, $start, $strLength) {
  if ($start === $strLength) {
    var_dump($str);
    return;
  }
  for ($i=$start; $i<$strLength; $i++) {
    swap($str, $i, $start);
    permute($str, $start+1, $strLength);
    swap($str, $start, $i);
  }
}
 
function swap(&$str, $pos1, $pos2) { 
  $tmp = $str[$pos1]; 
  $str[$pos1] = $str[$pos2]; 
  $str[$pos2] = $tmp; 
}