How can I have console output display to stdout AND store it in a variable?

Question

If I do this:

output = %x{some_script}

...then I have the stuff printed to stdout stored in output; but I don't see it appear on the screen.

On the other hand, if I do this:

success = system "some_script"

...then I see the output appear on the screen, but I don't have it stored in a variable (success just holds a boolean value).

Is there some way to get both? I'm aware I could do this:

output = %x{some_script}
puts output

But the problem there is that some_script might be a pretty long-running script, in which case I see nothing until the whole thing is finished. I'd prefer to see output as it's produced, and when it's finished to have it all stored in the output variable.

Answer 1

This is a solution with IO.popen:

require 'stringio'

output = StringIO.new

IO.popen("ls") do |pipe|
  pipe.each do |line|
    output.puts line
    puts line
  end
end

puts output.string # => Outputs the contents of `output` as a string

Answer 2

You could monkeypatch Kernel::puts, but I can only think of a kludgy global way to store the results:

class Kernel
  alias_method :old_puts, :puts
  def puts(*args)
    old_puts args
    $output << args
  end
end