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    ▪php中session文件过多inode用完，apache无法运行的解决方法      由于php程序中大量用到了session，php的session的采用默认的形式保存到/tmp中，服务器出现莫名的错误，主机bash上（本地上！远程看不到）反复提示类似错误： killed process 21034（apache2） out of memo.........

    ▪php通过文件头检测文件类型的自定义类      检测文件头信息，继而判断文件类型的例子，这个在防范上传不合要求的文件时，很有用的，比通过js判断文件类型的方法，安全多了。 代码如下：   代码示例: <?php /* 通过文件名，获得.........

    ▪php字符串截取substr函数简介      substr函数，用于字符串的截取。 substr(str,start,length); 例如： 代码示例: substr(php is very good language,4,5); 输出为 is ve; 1，当start>str的长度，则返回为（）；   代码示例: substr(php is very good lan.........

session.save_handler = files

代码示例:

session.save_handler = eaccelerator

代码示例:

session.save_path = "2;/tmp/session"
 

/tmp/session/0/0/
/tmp/session/0/1/
/tmp/session/0/3/
tmp/session/0/4/
……………………

代码示例:

find /tmp/session -amin +180 -exec rm -rf {} \;
 

代码示例:

<?php
/* 通过文件名，获得文件类型*
* @author chengmo*
* @version 0.1
* $filename="d:/1.png";echo cFileTypeCheck::getFileType($filename); 打印：png
* edit www.
*/
class cFileTypeCheck
{
private static $_TypeList=array();
private static $CheckClass=null;
private function __construct($filename)
{
self::$_TypeList=$this->getTypeList();
}
/**
*处理文件类型映射关系表*
*
* @param string $filename 文件类型
* @return string 文件类型，没有找到返回：other
*/
private function _getFileType($filename)
{
$filetype="other";
if(!file_exists($filename)) throw new Exception("no found file!");
$file = @fopen($filename,"rb");
if(!$file) throw new Exception("file refuse!");
$bin = fread($file, 15); //只读15字节 各个不同文件类型，头信息不一样。
fclose($file);
$typelist=self::$_TypeList;
foreach ($typelist as $v)
{
$blen=strlen(pack("H*",$v[0])); //得到文件头标记字节数
$tbin=substr($bin,0,intval($blen)); ///需要比较文件头长度
if(strtolower()($v[0])==strtolower(array_shift(unpack("H*",$tbin))))
{
return $v[1];
}
}
return $filetype;
}
/**
*得到文件头与文件类型映射表*
*
* @return array array(array(key,value)...)
*/
public function getTypeList()
{
return array(array("FFD8FFE1","jpg"),
array("89504E47","png"),
array("47494638","gif"),
array("49492A00","tif"),
array("424D","bmp"),
array("41433130","dwg"),
array("38425053","psd"),
array("7B5C727466","rtf"),
array("3C3F786D6C","xml"),
array("68746D6C3E","html"),
array("44656C69766572792D646174","eml"),
array("CFAD12FEC5FD746F","dbx"),
array("2142444E","pst"),
array("D0CF11E0","xls/doc"),
array("5374616E64617264204A","mdb"),
array("FF575043","wpd"),
array("252150532D41646F6265","eps/ps"),
array("255044462D312E","pdf"),
array("E3828596","pwl"),
array("504B0304","zip"),
array("52617221","rar"),
array("57415645","wav"),
array("41564920","avi"),
array("2E7261FD","ram"),
array("2E524D46","rm"),
array("000001BA","mpg"),
array("000001B3","mpg"),
array("6D6F6F76","mov"),
array("3026B2758E66CF11","asf"),
array("4D546864","mid"));
}
public static function getFileType($filename)
{
if(!self::$CheckClass) self::$CheckClass=new self($filename);
$class=self::$CheckClass;
return $class->_getFileType($filename);
}
}
?>

代码示例:

substr(php is very good language,4,5);
输出为 is ve;

代码示例:

substr(php is very good language,26,5);
substr(php is very good language,4);
输出为 （空白）
输出为is v (表明start和langth都为4)

代码示例:

substr(php is very good language,-4,5);
 

代码示例:

substr(php is very good language,4,-5);