PHP Warning system () has been disabled for security reasons

The code I am having a problem with is this: 

                        ob_start();

                        $resultTxt = system($command, $result);

                        $errTxt = ob_get_contents();

                        ob_clean();

                        $resultTxt = nl2br($errTxt) . "$resultTxt";

I get a PHP Warning that the system () has been disabled for security reasons. I don't have access to the php.ini file to change this.

Can the code be changed from system to something else that will work?