redirect_stdout_and_stderr.rb

RealStdOut = $stdout

# Replace the main thread's $stdout and $stderr with IO.pipes
# Create a thread to watch for data on the pipes
# call given block with IO name, timestamp, and data read from IO

def redirect_stdout_and_stderr_to &callback
  rout, $stdout = IO.pipe
  rerr, $stderr = IO.pipe
  map = { rout => 'stdout', rerr => 'stderr' }
  Thread.new do 
    buffer = ''
    ios = [ rout, rerr ]
    until ios.empty? do
      read, write = IO.select ios, []
      stamp = Time.now.to_f
      read.each do |io|
        begin
          io.readpartial 2048, buffer
          callback[map[io], stamp, buffer]
        rescue EOFError => e
          ios.delete io
          callback[map[io], stamp, "EOFError: #{e}"]
        end
      end
    end
  end
end

t = redirect_stdout_and_stderr_to do |name,stamp,message|
  RealStdOut.puts "#{name}-#{stamp}: #{message.inspect}"
end

puts :hi      # stdout-XXX2742887.3437052: "hi\n"
print :hi     # stdout-XXX2742888.5288196: "hi"
t.status      # => "sleep"
$stderr.close # stderr-XXX2742889.2119832: "EOFError: end of file reached"
t.status      # => "sleep"
$stdout.close # stdout-XXX2742890.3000205: "EOFError: end of file reached"
t.status      # => false