php怎么实现正则去掉空格

$str='
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$uuu=preg_replace("/(\s|\&nbsp\;|　|\xc2\xa0)/","",$str);
echo str_replace('<p></p>', '', $uuu);

　$html="<p>fdasf</p>";
　　echo $string = str_replace(array("<p>","","</p>"),"",$html);
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若是<p>     内容</p>替换成<p>内容</p><p>                 content</p>替换成<p>contend</p>（空格是tab键和空格键  混合的  都有可能）方法如下
　　$html=preg_replace('/[\n\r\t]/','',$html);//去空格
若是<p>后面跟了若干个，再是内容 
　　<p>     内容</p>
　　替换成<p>内容</p>
　　<p>   content</p>
　　替换成<p>contend</p>
　　<?php
　　$html="<p>
　　内容</p>替换成<p>内容</p>
　　<p>content</p>替换成<p>contend</p>";方法如下
　　$html=trim($html);
　　$html=str_replace(PHP_EOL,"",$html);
　　$html=str_replace(" ","",$html);
　　$html=preg_replace('/\s+/','',$html);
　　$html=preg_replace('/[\n\r\t]/','',$html);
　　echo "{$html}";
　　?>
str_replace("<p><br\/><\/p>","",$htmlstr);