正则表达式难题，，我想不出结果。。

Question

一段字符串中比如asd || as  sdsa er fdgd | wqeqw wqe|  werw||weq比如这样一个字符串，，我现在指定要用preg_replace替换其中的| 为>   ,注意|| 不能被替换，，请高手赐教

Answer 1

$str = 'asd || as sdsa er fdgd | wqeqw wqe| werw||weq';
echo preg_replace("/(?<!\|)\|(?!\|)/", '>', $str);
//asd || as sdsa er fdgd > wqeqw wqe> werw||weq

Answer 2

  1 <?php
  2 
  3 $str = 'asd || as sdsa er fdgd | wqeqw wqe| werw||weq';
  4 
  5 echo preg_replace('#(?>=\|)\|#m' , '-' , $str);
  6 ?>
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