文件签名一般都在文件的头部，如果你用十六进制方式查看文件，你就可以看到文件的一些签名信息。如用uestudio以十六进制方式查看zip格式的文件，其文件内容头部有50 4B 03 04这样的十六进制信息。同理jpg文件状况有FF D8 FF E0 xx xx 4A 46这样的十六进制信息，其实这此十六进制都是表示一些特殊字条。

php怎么样验证文件类型？先来看一个简单的方法：

function checkFileType($fileName){

$file = fopen($fileName, "rb");

$bin = fread($file, 2); //只读2字节

fclose($file);

// C为无符号整数，网上搜到的都是c，为有符号整数，这样会产生负数判断不正常

$strInfo = @unpack("C2chars", $bin);

$typeCode = intval($strInfo['chars1'].$strInfo['chars2']);

$fileType = '';

switch( $typeCode )

{

case '255216':

return $typeCode. ' : ' .'jpg';

break;

case '7173':

return $typeCode. ' : ' .'gif';

break;

case '13780':

return $typeCode. ' : ' .'png';

break;

case '6677':

return $typeCode. ' : ' .'bmp';

break;

case '7790':

return $typeCode. ' : ' .'exe';

break;

case '7784':

return $typeCode. ' : ' .'midi';

break;

case '8297':

return $typeCode. ' : ' .'rar';

break;

default:

return $typeCode. ' : ' .'Unknown';

break;

}

//return $typeCode;

}

$file_name = '11.doc';

echo checkFileType($file_name);

下来提供一个类的实现：

/*通过文件名，获得文件类型*

*@author chengmo QQ:8292669*

*@copyright http://www.cnblogs.com/chengmo 2010-10-17

*@version 0.1

*$filename="d:/1.png";echo cFileTypeCheck::getFileType($filename); 打印：png

*/

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);

}

}

$filename="22.jpg";

echo $filename,"t",cFileTypeCheck::getFileType($filename),"rn";

$filename="11.doc";

echo $filename,"t",cFileTypeCheck::getFileType($filename),"rn";

或者可以这么检测：

$filename = '22.jpg';

$extname = strtolower(substr($filename, strrpos($filename, '.') + 1));

echo $extname.'
';

$file = @fopen($filename, 'rb');

if ($file)

{

$str = @fread($file, 0x400); // 读取前 1024 个字节

echo substr($str, 0, 4);

@fclose($file);

}

if (substr($str, 0, 4) == 'MThd' && $extname != 'txt')

{

$format = 'mid';

}

elseif (substr($str, 0, 4) == 'RIFF' && $extname == 'wav')

{

$format = 'wav';

}

elseif (substr($str ,0, 3) == "/xFF/xD8/xFF")

{

$format = 'jpg';

}

elseif (substr($str ,0, 4) == 'GIF8' && $extname != 'txt')

{

$format = 'gif';

}

elseif (substr($str ,0, 8 ) == "/x89/x50/x4E/x47/x0D/x0A/x1A/x0A")

{

$format = 'png';

}

elseif (substr($str ,0, 2) == 'BM' && $extname != 'txt')

{

$format = 'bmp';

}

elseif ((substr($str ,0, 3) == 'CWS' || substr($str ,0, 3) == 'FWS') && $extname != 'txt')

{

$format = 'swf';

}

elseif (substr($str ,0, 4) == "/xD0/xCF/x11/xE0")

{ // D0CF11E == DOCFILE == Microsoft Office Document

if (substr($str,0x200,4) == "/xEC/xA5/xC1/x00" || $extname == 'doc')

{

$format = 'doc';

}

elseif (substr($str,0x200,2) == "/x09/x08" || $extname == 'xls')

{

$format = 'xls';

} elseif (substr($str,0x200,4) == "/xFD/xFF/xFF/xFF" || $extname == 'ppt')

{

$format = 'ppt';

}

} elseif (substr($str ,0, 4) == "PK/x03/x04")

{

$format = 'zip';

} elseif (substr($str ,0, 4) == 'Rar!' && $extname != 'txt')

{

$format = 'rar';

} elseif (substr($str ,0, 4) == "/x25PDF")

{

$format = 'pdf';

} elseif (substr($str ,0, 3) == "/x30/x82/x0A")

{

$format = 'cert';

} elseif (substr($str ,0, 4) == 'ITSF' && $extname != 'txt')

{

$format = 'chm';

} elseif (substr($str ,0, 4) == "/x2ERMF")

{

$format = 'rm';

} elseif ($extname == 'sql')

{

$format = 'sql';

} elseif ($extname == 'txt')

{

$format = 'txt';

}

echo $format;