这个preg_replace命令有什么问题？

Question

I have these codes:

$string = 'Hello [*tt();*], how are you today?';
preg_match("/\[\*(.*?)\*\]/",$string,$match);
$func = $match[1];
$d = eval($func);
$newstring = preg_replace("/\[\*(.*?)\*\]/",$d,$string);
echo $newstring;

function tt() {
     return 'test';
}

I think they reach my mean from them. I want to replace tt(); with its output.I expected it works but tt(); replace with nothing(null string).

Answer 1

From the PHP documentation: http://au2.php.net/manual/en/function.eval.php

eval() returns NULL unless return is called in the evaluated code, in which case the value passed to return is returned.

$d = eval("return $func");

eval should be used with caution. See When is eval evil in php?