Swift script that shows how to deliver notifications to OS X Notification Center using purely CLI. This can be pasted into a Playground and executed, too.

UserNotifications.swift

import Foundation

// Create a method that will be called instead of
// "bundleIdentifier()" that returns a non-empty
// bundle id, even for a CLI script
extension NSBundle {
    func fakeBundleIdentifier() -> NSString {
        if self == NSBundle.mainBundle() {
            return "dont.mind.me.totally.a.normal.bundleid"
        } else {
            return self.fakeBundleIdentifier()
        }
    }
}

// Method to dynamically swizzle the "bundleIdentifier()" method
// which the system will call on the main bundle with ours that
// returns a non-empty value
func swizzleToReturnANonEmptyBundleIdentifier() -> Bool {
    if let aClass = objc_getClass("NSBundle") as? AnyClass {
        method_exchangeImplementations(
            class_getInstanceMethod(aClass, "bundleIdentifier"),
            class_getInstanceMethod(aClass, "fakeBundleIdentifier")
        )
        return true
    }
    return false
}
swizzleToReturnANonEmptyBundleIdentifier()

//////////////////////////////////////////////////////////////////

// Now, the actual usage of notifications becomes very simple :)

func presentNotification(message: String) {
    let notification = NSUserNotification()
    notification.identifier = "\(NSDate().timeIntervalSince1970)"
    notification.title = "Title"
    notification.subtitle = "Subtitle"
    notification.informativeText = message

    NSUserNotificationCenter.defaultUserNotificationCenter().deliverNotification(notification)
}

presentNotification("Hi there! \(NSDate().timeIntervalSince1970)")

seems it break on mac 10.15:(