How come my adb can't simulate a touchscreen tap?

I've read I can simulate a tap on my touchscreen by using adb but it doesn't work:

C:\>adb shell input touchscreen tap 1 1
Error: Unknown command: touchscreen
usage: input [text|keyevent]
       input text 
       input keyevent 

How come I can't send a tap to my device? I have the latest version of the SDK tools and the SDK platform tools. Android Debug Bridge version 1.0.32. Thanks

Answer

Your version of SDK tools has nothing to do with the parameters input can understand or execute. Input is a binary in Android OS which can be run independently without requiring any set of external tools such as ADB.

The reason you receive the error "Error: Unknown command: touchscreen" is because you're running an Android version earlier than Android 4.1.1. You would already notice that in the input usage you posted, the binary entertains only two parameters i.e. text and keyevent.

In Android 4.0.x, the input command's usage remains the same as the one you posted. In fact, even Android 2.3.7 has the same input command's usage. (See com.android.commands.input.Input on GrepCode for comparison of command's usage between Android versions.)

It was Android 4.1.1 which introduced tap and swipe parameter with usage,

usage: input ...
       input text 
       input keyevent 
       input tap  
       input swipe    

See the source code for more.