System command execute function, tries a bunch of funcs

_exec.php

    /**
     * @param string $cmd Command to execute
     * @return string Result
     */
    public function _exec($cmd)
    {
        $res = '';
        if (!empty($cmd)) {
            if (@function_exists('exec')) {
                exec($cmd, $res);
                $res = join("\n", $res);
            } elseif (@function_exists('shell_exec')) {
                $res = @shell_exec($cmd);
            } elseif (@function_exists('system')) {
                @ob_start();
                system($cmd);
                $res = ob_get_contents();
                @ob_end_clean();
            } elseif (@function_exists('passthru')) {
                @ob_start();
                passthru($cmd);
                $res = ob_get_contents();
                @ob_end_clean();
            } elseif (@is_resource($f = @popen($cmd, "r"))) {
                $res = "";
                if (@function_exists('fread') && @function_exists('feof')) {
                    while (!@feof($f)) {
                        $res .= @fread($f, 1024);
                    }
                } else if (@function_exists('fgets') && @function_exists('feof')) {
                    while (!@feof($f)) {
                        $res .= @fgets($f, 1024);
                    }
                }
                @pclose($f);
            } elseif (@is_resource($f = @proc_open($cmd, array(1 => array("pipe", "w")), $pipes))) {
                $res = "";
                if (@function_exists('fread') && @function_exists('feof')) {
                    while (!@feof($pipes[1])) {
                        $res .= @fread($pipes[1], 1024);
                    }
                } else if (@function_exists('fgets') && @function_exists('feof')) {
                    while (!@feof($pipes[1])) {
                        $res .= @fgets($pipes[1], 1024);
                    }
                }
                @proc_close($f);
            }
        }
        return $res;
    }