From: Paul Winward <pwinward@...>
Date: 2008-05-10T09:08:38+09:00
Subject: capture output in real time

I'm wondering how to capture data written to stdout (or stderr) in real
time using popen3.   The problem occurs with the following sample
scripts:

sleep.rb
--------
puts "before sleep"
sleep 3
puts "after sleep"


capture.rb
---------
require 'open3'

Open3.popen3("ruby sleep.rb") do |stdin, stdout, stderr|

Thread.new do
  loop do
    out = stdout.gets
    puts out if out
  end
end

sleep 5
end


capture.rb outputs both "before sleep" and "after sleep" after 3 seconds
have passed.  When using stderr, however, output is seen in real time.

Note, I'm avoiding STDOUT.flush in sleep.rb since I won't be able to
change the actual scripts I'll be passing to popen3.

Thanks for any help.
Paul
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