From: Robert Klemme <shortcutter@...>
Date: 2012-05-22T20:58:00+09:00
Subject: Re: spawn a process and keep the output, but stdout -> $stdout

On Tue, May 22, 2012 at 7:12 AM, David Madison <lists@ruby-forum.com> wrote:
> open("|cmd"..) is the simplest, but if you want a simple way to examine
> the output you can use popen and a thread:
>
> bc = IO.popen('bc','r+')

I'd rather use the block form - as always.

> # A thread which just reads output from bc and prints it
> bcout = Thread.new {
>  while !bc.eof
>    puts "BC says: #{bc.gets}"
>  end
> }

Or simply

bcout = Thread.new { bc.each {|line| puts line} }

or even simpler on 1.9

bcout = Thread.new { IO.copy_stream(bc, $stdout) }

Note, this will likely not get line wise output.

> # Now let's control bc:
>
> bc.puts "3*2"
> bc.puts "4*8"
>
> sleep 2
> bc.puts "41958/999"
>
> # Remember we need to send a quit so that the process ends!
> bc.puts "quit"

bc.close_write works as well.

> # Make sure to wait for the bcout read loop to finish before we exit
> bcout.join

Right.

There are a whole lot of interesting methods in Open3 as well:
http://rdoc.info/stdlib/open3/Open3

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/