$str = 'Hello_world!';
$chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789/-';
$result = array_reduce(str_split($str),
  fn($carry, $item)=>$carry.=$item.$chars[rand(0,strlen($chars)-1)], '');
print_r($result);

str_split将您的输入字符串拆分为字符，然后array_reduce将它们与添加的随机字符重新组合。

<?PHP
  $str =  "Hello World!";

  $new_string = '';
  for($i =0; $i < strlen($str); $i++){ // loop through the string
     $new_string .= $str[$i]; // add character to new string
     $new_string .= getRandomCharacter(); // add the random character to new string
  }
  echo $new_string;

  function getRandomCharacter(){
     $random_characters = 'abcdefghijklmnopqrstuvwxyz'
                 .'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
                 .'0123456789!@#$%^&*()';
    $index= rand(0, (strlen($random_characters)- 1) ); // generates random character index from the given set.
    return $random_characters[$index];
  }

?>