private function _findBinary($name)
    {
        $binary = '';

        if ($this->_isDarwin) {
            $locations = array(
                '/opt/local/bin/', // MacPorts
                '/usr/local/bin/', // Mac GPG
                '/sw/bin/',        // Fink
                '/usr/bin/'
            );
        } else {
            $locations = array(
                '/usr/bin/',
                '/usr/local/bin/'
            );
        }

        foreach ($locations as $location) {
            if (is_executable($location . $name)) {
                $binary = $location . $name;
                break;
            }
        }

        return $binary;
    }