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.

Hector Castro · Accepted Answer · 2011-09-01 21:31:02Z

9

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

answered Sep 1, 2011 at 21:31

Hector Castro

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4 Comments

mu is too short Over a year ago

Or use popen3 if the standard error stream is also desired.

Dan Tao Over a year ago

Am I missing something? This also appears to wait until the command has finished executing, much like the %x{} + puts option.

mu is too short Over a year ago

@Dan: Sounds like you have a buffering problem.

Dan Tao Over a year ago

My mistake: I used an overly simplistic script to test this on; after taking the hint from @mu and actually trying it on my real script, I see that it works. Thanks!

wersimmon · Accepted Answer · 2011-09-02 03:14:24Z

1

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

answered Sep 2, 2011 at 3:14

wersimmon

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