From: Jean-Julien Fleck <jeanjulien.fleck@...>
Date: 2010-07-17T21:05:15+09:00
Subject: Driving irb from IO.popen

Hello,

I'm stuck with a problem concerning IO.popen
It's not necessarily related to irb but that's a good point where to start.

I'd like to drive irb from ruby using IO.popen. The problem is: each
time I type something inside irb, I can get one, two or more lines of
output I'd like to store with no way to know beforehand how many there
will be.

The thing is: I don't know how to detect when irb has ended its output
and is waiting for me to give some input.

I tried the following:

  def irb(string)
    output = ''
    puts "Trying to talk to irb"
    IO.popen('irb --simple-prompt','r+') do |io|
      string.chomp.split.each do |s|
        io.puts s
        while line = io.gets
          line = io.gets
          puts line
          output += line
        end
      end
    end
    return output
  end

  s = "2+2\n'2'+'2'\n'2'+2"

  irb(s)

I was hoping that io.gets would be nil when irb is waiting for input,
but it's not. So this little program gets stuck after the first
statement:

brisingr ~/tmp>ruby essai_irb.rb
Trying to talk to irb
=> 4

Rather, I would like him to return

>> 2+2
=> 4
>> '2'+'2'
=> "22"
>> '2'+2
TypeError: can't convert Fixnum into String
        from (irb):4:in `+'
        from (irb):4

Does someone have a workaround ?

Thanks,

-- 
JJ Fleck
PCSI1 Lycée Kléber