php如何去除空行

<?php
$str="i am a book




moth";
//去除所有的空格和换行符
echo preg_replace("/[s]{2,}/","",$str).'<br>';
//去除多余的空格和换行符，只保留一个
echo preg_replace("/([s]{2,})/","1",$str);
//去除多余的空格或换行 $text = preg_replace("/(
|
|
|	)/i", '', $text);
$lastSeveralLineContentsArr = preg_replace("/([ |	]{0,}[
]{1,}){2,}/","",$lastSeveralLineContentsArr);
//对Html里有连续的空行或tab给正则过滤掉>
?>