NSAppleEventManager.shared().setEventHandler(self, andSelector: #selector(handleGetURLEvent(event:withReplyEvent:)), forEventClass: AEEventClass(kInternetEventClass), andEventID: AEEventID(kAEGetURL))

@objc func handleGetURLEvent(event: NSAppleEventDescriptor!, withReplyEvent: NSAppleEventDescriptor!) {
    if let text = event.paramDescriptor(forKeyword: AEKeyword(keyDirectObject)) {
        // you may want to filter the commands here
        if text.contains("yourScheme://doStuff") {

        } else if ...
    }
}

$ open "yourScheme://doStuff"
$ open "yourScheme://doSomethingElse"