将多个连续的换行符替换成一个

<?php
include "../../config.php";

$msg = "AAAAAAAAAA

BBBBBBBBBB

CCCCCCCCCC

DDDDDDDDDD

EEEEEEEEEE

FFFFFFFFFF";
//p_val($msg);

//多个换行符替换成一个换行符
$pattern = '(\s+\r)';
p_val("-----------处理前-----------");
p_val($msg);
$msg = preg_replace($pattern, "\n", $msg);
p_val("-----------处理后-----------");
p_val($msg);
?>