After asking this question, it looks like I need to use Ruby's PTY Module, of which there is no documentation.

I have written this code to try to push content to Google App Engine because the python command sometimes asks me for my username and password. But when I run this code, it just hangs.

cmd = "appcfg.py update cdn"
PTY.spawn("#{cmd} 2>&1") do | input, output, pid |
  begin
    input.expect("Email:") do
      output.write("#{credentials[:username]}\n")
    end
    input.expect("Password:") do
      output.write("#{credentials[:password]}\n")
    end
  rescue Exception => e
    puts "GAE Error..."
  end
end

What am I missing here? How can I get this to work?