<?php
 /**
  * 压缩html : 清除换行符,清除制表符,去掉注释标记  
  * @param   $string  
  * @return  压缩后的$string 
  * */
 function compress_html($string) {  
     $string = str_replace("rn", '', $string); //清除换行符  
     $string = str_replace("n", '', $string); //清除换行符  
     $string = str_replace("t", '', $string); //清除制表符  
     $pattern = array (  
                     "/> *([^ ]*) *</", //去掉注释标记  
                     "/[s]+/",  
                     "/<!--[^!]*-->/",  
                     "/" /",  
                     "/ "/",  
                     "'/*[^*]**/'" 
                     );  
     $replace = array (  
                     ">1<",  
                     " ",  
                     "",  
                     """,  
                     """,  
                     "" 
                     );  
     return preg_replace($pattern, $replace, $string);  
 }

<?php
$str="i   am    a     booknnnnnmoth";
//去除所有的空格和换行符
echo preg_replace("/[s]{2,}/","",$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);
?>

<?php
// $document 应包含一个 HTML 文档。
// 本例将去掉 HTML 标记，javascript 代码
// 和空白字符。还会将一些通用的
// HTML 实体转换成相应的文本。

$search = array ("'<script[^>]*?>.*?</script>'si",  // 去掉 javascript
                 "'<[/!]*?[^<>]*?>'si",           // 去掉 HTML 标记
                 "'([rn])[s]+'",                 // 去掉空白字符
                 "'&(quot|#34);'i",                 // 替换 HTML 实体
                 "'&(amp|#38);'i",
                 "'&(lt|#60);'i",
                 "'&(gt|#62);'i",
                 "'&(nbsp|#160);'i",
                 "'&(iexcl|#161);'i",
                 "'&(cent|#162);'i",
                 "'&(pound|#163);'i",
                 "'&(copy|#169);'i",
                 "'&#(d+);'e");                    // 作为 PHP 代码运行

$replace = array ("",
                  "",
                  "1",
                  """,
                  "&",
                  "<",
                  ">",
                  " ",
                  chr(161),
                  chr(162),
                  chr(163),
                  chr(169),
                  "chr(1)");

$text = preg_replace ($search, $replace, $document);
?>