PHP 系统命令函数

function execute($cmd) {
    $res = '';
    if ($cmd) {
        if(function_exists('system')) {
            @ob_start();
            @system($cmd);
            $res = @ob_get_contents();
            @ob_end_clean();
        } elseif(function_exists('passthru')) {
            @ob_start();
            @passthru($cmd);
            $res = @ob_get_contents();
            @ob_end_clean();
        } elseif(function_exists('shell_exec')) {
            $res = @shell_exec($cmd);
        } elseif(function_exists('exec')) {
            @exec($cmd,$res);
            $res = join(“
",$res);
        } elseif(@is_resource($f = @popen($cmd,"r"))) {
            $res = '';
            while(!@feof($f)) {
                $res .= @fread($f,1024);
            }
            @pclose($f);
        }
    }
    return $res;
}