How to use System Clipboard input in Execute Shell Script

Execute Shell Script has an option to use input from "System Clipboard". I couldn't figure out how to actually use that input. And it doesn't seem to be "$1".

What is the correct way to refer to the input coming from System Clipboard in the script?

thank you

Whichever way you choose to supply input to the shell script action (see the KM wiki action:Execute a Shell Script [Keyboard Maestro Wiki]) it is "fed" into stdin so that's where your clipboard contents appears to your script.