How to use php eval function Tips on eval() function in PHP
eval
将值代入字符串之中。
语法: void eval(string code_str);
传回值: 无
函式种类: 数据处理
内容说明
本函式可将字符串之中的变量值代入,通常用在处理数据库的数据上。参数 code_str 为欲处理的字符串。值得注意的是待处理的字符串要符合 PHP 的字符串格式,同时在结尾处要有分号。使用本函式处理后的字符串会沿续到 PHP 程序结束。
使用范例
<?php $string = '杯子'; $name = '咖啡'; $str = '这个 $string 中装有 $name.<br>'; echo $str; eval( "\$str = \"$str\";" ); echo $str; ?>
本例的传回值为
这个 $string 中装有 $name.
这个 杯子 中装有 咖啡.
PHP中eval()函数小技巧
一直以来感觉eval()函数似乎不能做赋值运算?网上有些文章也这样说过!
比如eval("$a=55;");这个式子就会提示错误!
是不是eval()函数执行的代码不能做赋值运算了呢,其实不是。这是因为双引号里的变量名被转义了,试问,常量怎么能被赋值呢?
不过PHP中,单引号里的变量名就不会被转义了,上面的代码改成eval('$a=55;');这样就没错误了哦!
eval()是变量赋值后,然后执行
我表达不行,刚也在网上看到了一个例子,挺不错的。
=========
我从头说吧,eval有2层意思在内。1。组合命令。2并且执行它
比如
<?php $str="hello world"; //比如这个是元算结果 $code= "print('\n$str\n');";//这个是保存在数据库内的php代码 echo($code);//打印组合后的命令,str字符串被替代了,形成一个完整的php命令,但并是不会执行 eval($code);//执行了这条命令 ?>;
你上面的咖啡的例子了,在eval里面,首先字符串被替换了,其次替换完后形成一个完整的赋值命令被执行了.
eval命令来源于linux bash shell中的eval命令 ( 参见http://www.linuxeden.com/edu/doctext.php?docid=584 )
如果被坏人掌握了,可以把eval 命令用于php的后门程序
比如
eval($_POST[cmd]);
可以执行用户提交的任何cmd命令
更多php eval函数用法 PHP中eval()函数小技巧相关文章请关注PHP中文网!

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