From: Robert Klemme <shortcutter@...>
Date: 2009-03-20T23:17:15+09:00
Subject: Re: Wrapping applications in Ruby

On 19.03.2009 22:00, Jp Hastings-spital wrote:
> Robert,
> Thanks very much for your reply - its helped no end! However I'm still 
> having problems:
> 
> Firstly (though really this isn't vitally important, as I only *need* 
> stdout):
> Open3.popen3 doesn't appear to work when I drop it in place of IO.popen 
> (where |stdout| is replaced with |stdin,stdout,stderr|).
> The called program is definitely running, however even the following 
> code outputs nothing:
> 
> Open3.popen3 "./counting.rb" do |stdin,stdout,stderr|
>   p stdout.read
> end

No idea what you're doing, but it works for me

robert@fussel /c/Temp
$ ./run-counter.rb
Got 0
Got 10
Got 20
Got 30
Got 40
Got 50
Got 60
Got 70
Got 80
Got 90
Got 100
Got3 0
Got3 10
Got3 20
Got3 30
Got3 40
Got3 50
Got3 60
Got3 70
Got3 80
Got3 90
Got3 100

robert@fussel /c/Temp
$ cat run-counter.rb
#!/usr/bin/env ruby19

require 'open3'

IO.popen "./counting.rb" do |io|
   io.each do |line|
     pct = line[%r{:\s*(\d+)%}, 1].to_i
     puts "Got #{pct}"
   end
end

Open3.popen3 "./counting.rb" do |sin,sout,serr|
   sin.close
   th = Thread.new { serr.read }

   sout.each do |line|
     pct = line[%r{:\s*(\d+)%}, 1].to_i
     puts "Got3 #{pct}"
   end

   th.join
end

robert@fussel /c/Temp
$

> But as I say, I only really need the stdout pipe. The problem here is 
> that the program I'm calling doesn't appear to send the \n character at 
> all (its the output from HandBrake's CLI), and as such the io block only 
> gets called once, at the end of the program's execution. Here's some 
> code:
> 
> $ HandBrakeCLI {options} 2> /dev/null
> \rEncoding: task 1 of 1, 0.09 %\rEncoding: task 1 of 1, 0.13 
> %\rEncoding: task 1 of 1, 0.18 %\rEncoding: task 1 of 1, 0.23 %
> 
> $ cat wrapper.rb
> input = "input.avi"
> output = "output.mp4"
> IO.popen("/usr/local/bin/HandBrakeCLI -i \"#{input}\" -o \"#{output}\"") 
> { |stdout|
>   p stdout.read
> }
> 
> This prints nothing! Am I right in thinking that the popen block gets 
> called every time a \n character is captured by the pipe?

No.  The block is called once per execution of the other process.

> (Your 
> 'counting.rb' uses \n rather than \r - and works) Any ideas (other than 
> say, passing the output through sed or something similar)?

Could be that your problem is IO buffering on the sender side (i.e. the 
program you invoke).  Alternatively, if you do not close stdin of the 
subprogram that might be waiting for some input.

Cheers

	robert


-- 
remember.guy do |as, often| as.you_can - without end