From: Brian Candler <b.candler@...>
Date: 2010-06-17T05:15:03+09:00
Subject: Re: Simulating keystrokes for automated user input

Ryan Mohr wrote:
> Brian Candler wrote:
>> Spawn a pty. There's pty.so in the standard library, which is a C 
>> extension and unfortunately not well documented, but google for 
>> "PTY.spawn" to find some examples, e.g.
> 
> Thanks for the suggestion Brian but I don't think that will work for my 
> case.  I need to send keystrokes to stdin of the current process itself.

Then I think you're stuck. When your ruby process was started, its stdin 
file descriptor was connected to something (e.g. a terminal or a pipe). 
Only that thing can generate data for your app to read; e.g. you can't 
write to the read end of a pipe.

You could connect forcibly reopen stdin on a different fd:

  rd, wr = IO.pipe
  STDIN.reopen(rd)
  Thread.new do
    wr.puts "hello"
  end
  line = gets
  puts line.inspect

That's really horrible though. It would be better to fork your program 
entirely:

  IO.popen("-","rb+") do |pipe|
    if pipe
      # parent
      pipe.puts "hello"
      res = pipe.gets
      puts "got: #{res}"
    else
      # child
      line = gets
      puts line.inspect
    end
  end

If what you're trying to accomplish is unit testing of a CLI-driven 
program, then I'd suggest either running the program under test as a 
child (e.g. using IO.popen or PTY.spawn), or factor out your objects so 
that they can read and write to arbitrary IO objects that you pass in, 
so that you can pass them a StringIO or one end of a pipe.

Otherwise, perhaps you can explain what you are trying to achieve?

Regards,

Brian.
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