I'm not sure if there is already some way to do this or not, but when I run a sketch with "rp5 run sketch.rb" I'd like to be able to output lines of logging text to the command line while the sketch is running.  I've tried puts "some text" and $app.print_ln "some text", but neither seems to show any output.  Short of adding an in sketch display, I can't think of another way of showing debug style output.