php trim 删除空格字符与指定字符

<?php 
$str = " this line containstliberal rn use of whitespace.nn"; 
// first remove the leading/trailing whitespace  
//去掉开始和结束的空白  
$str = trim($str); 
// now remove any doubled-up whitespace  
//去掉跟随别的挤在一块的空白  
$str = preg_replace(&#39;/s(?=s)/&#39;, &#39;&#39;, $str); 
// finally, replace any non-space whitespace, with a space  
//最后，去掉非space 的空白，用一个空格代替  
$str = preg_replace(&#39;/[nrt]/&#39;, &#39; &#39;, $str); 
echo "<pre class="brush:php;toolbar:false">{$str}