Since I know nothing about Ruby, I reply only in the wait of a knowledgeable answer...
I see such absence of output on Windows, when running a GUI program: it is not attached to a console, so stdout printing goes to void. It is the case of sketches exported as applications, for example.
In this case, a solution is to use a logger. Either Java's built in one, or more simply open a file in text mode and direct your output to it. Less immediate result (but you can use tail -f on the file, if you are on Unix or if you have something like UnxUtils installed) but effective.

Thanks for your reply, phi.lho!  I like the idea of creating a logger class that logs to a file.  It would be nice to have a more advanced logging system.  However, for situations that require something quick and easy, I figured out that you can just print out stuff out in the terminal if you use standard error to puts the message, like so: