php安装向导中判断是否安装的实现思路

if(!defined('SYSDIR')) header('Location: ./install/');

                // write config file last off in case installation fails
                $configfile="<?php if(!defined('ROOT')) die('Access denied.');

\$servername  = '$servername';
\$dbname      = '$dbname';
\$dbusername  = '$dbusername';
\$dbpassword  = '$dbpassword';
\$dbmysql  = '$dbmysql';

define('TABLE_PREFIX', '$tableprefix');
define('COOKIE_KEY', '".PassGen(12)."');
define('WEBSITE_KEY', '".PassGen(12)."');
define('SYSDIR', '$SYSDIR');

?>";

                // write the config file
                $filenum = fopen (ROOT . "config/config.php","w");
                ftruncate($filenum, 0);
                fwrite($filenum, $configfile);
                fclose($filenum);