The **iw scan** command is used to scan for wireless networks
visible to a wireless interface. For convenience, the networks are
sorted by signal strength.

@static
@category iw
@param {string} interface The wireless network interface.
@param {function} callback The callback function.
function scan(options, callback) {
  var interface, show_hidden
  if (typeof options === 'string') {
    var interface = options;
    var show_hidden = false;
  } else {
    var interface = options.iface;
    var show_hidden = options.show_hidden || false;
  }

  this.exec('iw dev ' + interface + ' scan', parse_scan(show_hidden, callback));
}