string_rotate_working.php

<?php
  define('DEBUG', isset($argv[2]) && strtolower($argv[2]) == '--debug'); // just set the last one to "--debug"

  $locale = explode('.', getenv('LC_ALL'))[1];
  echo sprintf('System locale: %s [mb_internal_encoding set to: %s]' . "\n", getenv('LC_ALL'), $locale);

  function rotateStringSimple(string $str) : string {
    $res = '';

    if (DEBUG) echo sprintf('%s String length: %s' . "\n", __FUNCTION__, strlen($str));

    for ($i = 0; $i < strlen($str); $i++) {
      $chr = $str{$i};
      $res = $chr . $res;

      if (DEBUG) {
        echo sprintf('%s: Rotated hex value: %s [%s]' . "\n", __FUNCTION__, bin2hex($chr), $chr);
      }
    }
    return $res;  
  }

  function rotateStringMb(string $str) : string {
    $res = '';

    if (DEBUG) echo sprintf('%s String length: %s' . "\n", __FUNCTION__, mb_strlen($str));

    for ($i = 0; $i < mb_strlen($str); $i++) {
      $chr = mb_substr($str, $i, 1);
      $res = $chr . $res;

      if (DEBUG) {
        echo sprintf('%s: Rotated hex value: %s [%s]' . "\n", __FUNCTION__, bin2hex($chr), $chr);
      }
    }
    return $res; 
  }

  /**
   * This one will work for this purpose
   */
  function rotateStringGrapheme(string $str) : string {
    $res = '';

    if (DEBUG) echo sprintf('%s: String length: %s' . "\n", __FUNCTION__, grapheme_strlen($str));

    for ($i = 0; $i < grapheme_strlen($str); $i++) {
      $chr = grapheme_substr($str, $i, 1);
      $res = $chr . $res;

      if (DEBUG) {
        echo sprintf('%s: Rotated hex value: %s [%s]' . "\n", __FUNCTION__, bin2hex($chr), $chr);
      }
    }
    return $res;
  }
  
  $str = $argv[1]; // shell call: $ ~ php script.php argument -- "argument" is in the 2nd pos

  echo sprintf('Your string reversed (sb): %s' . "\n", rotateStringSimple($str));
  echo sprintf('Your string reversed (mb): %s' . "\n", rotateStringMb($str));
  echo sprintf('Your string reversed (gp): %s' . "\n", rotateStringGrapheme($str));