From: ara.t.howard@...
Date: 2006-05-24T02:43:08+09:00
Subject: Re: IRB'ing within a program

On Wed, 24 May 2006, Geoff Stanley wrote:

> Logan and Hal, this sounds like a good idea. However, as Logan's code
> illustrated, pipes are difficult to get working right. I was just
> playing around with them myself; I've discovered a few problems that
> might not be overcome.
>
> First, the code that I was using:
>    irb = IO.popen('irb', 'r+')
>    loop do
>        print ">> "
>        irb.puts gets
>        irb.gets        # Gets the line that we just put.
>        puts "=> #{irb.gets.chomp.inspect}"
>    end
>
> Now, the problems:
> 1) Everything we get back is a string. 1+2 should return the Fixnum 3,
> but we read that Fixnum 3 through the pipe as a string. To overcome
> this, we'd have to know what type of value we should get in return.
> That's basically redoing a good portion of irb.
>
> 2) This code doesn't get lines in the right proportion. It works for
> basic things like '1+2' and 'foo = 42', but for a multiline piece of
> code, such as a method definition, it breaks down:
>    >> def foo
>       puts "bar"
>    end
>    foo
>    ....... hello?
> As you can see, I got no output back.
>
> Any way popen could be used more effectively? I don't want to have to
> reimplement irb -- that would be a lot of work, I imagine.

you are trying way to hard:

   harp:~ > cat a.rb
   system 'irb'
   puts 'done'


   harp:~ > ruby a.rb
   irb(main):001:0> def foo
   irb(main):002:1> 42
   irb(main):003:1> end
   => nil
   irb(main):004:0> foo
   => 42
   irb(main):005:0> exit
   done

irb uses readline so you need to use pty to control it.  otherwise you'll not
see the prompt.

-a
-- 
be kind whenever possible... it is always possible.
- h.h. the 14th dali lama