Making a flashing console message with ruby

Question

0.upto(9) do
    STDOUT.print "Flash!"
    sleep 0.5
    STDOUT.print "\b\b\b\b\b\b" # (6 backspaces, the length of "Flash!")
    sleep 0.5
end

This code doesn't work. It prints Flash! to the screen, but it doesn't flash. It just stays there, as though the backspaces aren't taking effect. But I do this:

0.upto(9) do
    STDOUT.print "Flash!"
    sleep 0.5
    STDOUT.print "\b\b\b\b\b" # (5 backspaces, the length of "Flash! - 1")
    sleep 0.5
end

and it almost works. It prints this: FFFFFFFFFFlash!(after 9 loops) Why do the backspaces stop taking effect when their number is equal to the length of the string they're deleting?

How can I overcome this problem and create a flashing message, only using libraries that are part of rails?

I tried a workaround like this:

0.upto(9) do
    STDOUT.print " Flash!"
    sleep 0.5
    STDOUT.print "\b\b\b\b\b\b"
    sleep 0.5

end

(Note the space in " Flash!"), but what happens is the message appears to crawl across the screen! An interesting effect, but not what I want.

I'm using Command Prompt with Ruby and Rails in Windows 7

Answer 1

Typically this would be written something like:

0.upto(9) do
  STDOUT.print "\rFlash!"
  sleep 0.5
  STDOUT.print "\r      " # Send return and six spaces
  sleep 0.5
end

Back in the days when we'd talk to TTY and dot-matrix printers, we'd rapidly become used to the carriage-control characters, like "\r", "\n", "\t", etc. Today, people rarely do that to start, because they want to use the web, and browsers; Learning to talk to devices comes a lot later.

"\r" means return the carriage to its home position, which, on a type-writer moved the roller all the way to the right so we could start typing on the left margin again. Printers with moving heads reversed that and would move the print-head all the way to the left, but, in either case, printing started on the left-margin again. With the console/telnet/video-TTY, it moves the cursor to the left margin. It's all the same, just different technology.

---

A little more usable routine would be:

msg = 'Flash!'

10.times do
  print "\r#{ msg }"
  sleep 0.5
  print "\r#{ ' ' * msg.size }" # Send return and however many spaces are needed.
  sleep 0.5
end

Change msg to what you want, and the code will automatically use the right number of spaces to overwrite the characters.

Answer 2

Anyway, it looks like backspace (at least in windows) just positions the cursor back, you need/want to overwrite the character with a space at that point (or 6 of them) to "blank" the text out.