Problem Statement

Obtain a valid   Y   or   N   response from the keyboard. The keyboard should be flushed, so that any outstanding key-presses are removed, preventing any existing   Y   or   N   key-press from being evaluated. The response should be obtained as soon as   Y   or   N   are pressed, and there should be no need to press an   enter   key.

Let's start with the solution:

for  read !,"Enter Y or N to continue: ",input  quit:input?1(1"Y",1"y",1"N",1"n")