In a lot of cases you're better off using str_repeat if you want to use something like   - it repeats the entire string.

Using str_repeat, I wrote a full string pad function that should closely mimic str_pad in every other way:

<?php
function full_str_pad($input, $pad_length, $pad_string = '', $pad_type = 0) {
 $str = '';
 $length = $pad_length - strlen($input);
 if ($length > 0) { // str_repeat doesn't like negatives
  if ($pad_type == STR_PAD_RIGHT) { // STR_PAD_RIGHT == 1
   $str = $input.str_repeat($pad_string, $length);
  } elseif ($pad_type == STR_PAD_BOTH) { // STR_PAD_BOTH == 2
   $str = str_repeat($pad_string, floor($length/2));
   $str .= $input;
   $str .= str_repeat($pad_string, ceil($length/2));
  } else { // defaults to STR_PAD_LEFT == 0
   $str = str_repeat($pad_string, $length).$input;
  }
 } else { // if $length is negative or zero we don't need to do anything
  $str = $input;
 }
 return $str;
}

$pad_me = "Test String";
echo '|'.full_str_pad($pad_me, 20, ' ')."|\n";
echo '|'.full_str_pad($pad_me, 20, ' ', STR_PAD_RIGHT)."|\n";
echo '|'.full_str_pad($pad_me, 20, ' ', STR_PAD_BOTH)."|\n";
?>