From: Alexy Khrabrov <deliverable@...>
Date: 2007-11-10T07:34:31+09:00
Subject: Re: background process readling lines and responding

Hey Szymon -- good to see you here!  If, instead of "grep something", I 
give it a Ruby program which reads and writes lines, it works OK.  I 
wonder what's different between these:

-- a.rb:
IO.popen("ruby b.rb", "r+") do |f|
  STDIN.each_line do |x|
    @write = f.puts x.to_s
    @read = f.gets
    puts "back: #{@read}"
  end
end

-- b.rb:
STDOUT.sync = true

def readWrite
  while @string = gets
    @string.chomp!
    puts "received => #{@string}"
  end
end

readWrite

$ ruby a.rb
/z/aha/ru/popen ruby a.rb
abra
back: received => abra
cadabra
back: received => cadabra
...
-- can enter strings, they're echoed back.

Now, let's call "grep abra" instead of b.rb:
-- call-grep.rb:
IO.popen("grep abra", "r+") do |f|
  STDIN.each_line do |x|
    puts "sending: #{x}"
    @write = f.puts x.to_s
    @read = f.gets
    puts "back: #{@read}"
  end
end

$ ruby call-grep.rb:
/z/aha/ru/popen ruby call-grep.rb
abra
sending: abra
cadabra
-- already unresponsive.
-- 
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