PHP 敏感词替换

<?php
header("content-type:text/html;charset=utf-8");

$content= "直接进行排序，绿色字体为未排序问";

$arr = file("./sensitive_word.txt");   //一个敏感词一行
$arr1 = array();
foreach($arr as $k=>$v){
   $arr1["num".$k] = trim($v);
}


echo $content = str_replace($arr1,"*",$content);