Preg_replace Rotate PHP Code

Preg_replace replacing PHP code
There is a PHP code, I want to make all the characters between uppercase and lowercase

PHP Code

  
  A = "
  
   ; Echo preg_replace ("/(. *?) <\/a>/es "," "". Strtoupper ("\\1"). "" ', $a);

The result of the output is always incorrect, always take some strings as PHP code execution (such as the output of the result $str lost), how can I output the correct results? Or is there any other way to achieve this?

Thanks, man.

------Solution--------------------

PHP Code

$a = "
  
   ; Echo preg_replace_callback ("/(. *?) <\/a>/s ", ' foo ', $a); function foo ($r) {  
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