How to set up configuration files in PHP

function set_config($config){
        if(!is_array($config)) return FALSE;
        $configfile = CONF_PATH.'config.php';
        if(!is_writable($configfile)) return('Please chmod ./config.inc.php to 0777 !');
        $pattern = $replacement = array();
        $str = file_get_contents($configfile);
        foreach($config as $k=>$v){
            $pattern[$k] = "/['\"]".strtoupper($k)."['\"]\s*=>\s*([']?)[^']*([']?)/is";
            $replacement[$k] = "'".strtoupper($k)."'=> \${1}".$v."\${2}";
        }
         
        $str = preg_replace($pattern, $replacement, $str);
        return file_put_contents($configfile, $str);
    }