From: Robert Klemme <shortcutter@...>
Date: 2009-03-20T23:57:14+09:00
Subject: Re: Wrapping applications in Ruby


Few more remarks:

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

This will read the whole stream to the end!  Which means, it will return 
only after the process died.

> end
> 
> 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 %

If you have "\r" as line terminator, you can do the reading like this

io.each "\r" do |line|
   # do whatever with line
end

e.g.

robert@fussel ~
$ ruby -e '3.times {|i| printf "%03d\r", i}' | ruby -e 
'$stdin.each("\r") {|l| p l}'
"000\r"
"001\r"
"002\r"

robert@fussel ~
$

> $ cat wrapper.rb
> input = "input.avi"
> output = "output.mp4"
> IO.popen("/usr/local/bin/HandBrakeCLI -i \"#{input}\" -o \"#{output}\"") 
> { |stdout|
>   p stdout.read

See above.

> }
> 
> This prints nothing! Am I right in thinking that the popen block gets 
> called every time a \n character is captured by the pipe? (Your 
> 'counting.rb' uses \n rather than \r - and works) Any ideas (other than 
> say, passing the output through sed or something similar)?
> 
> Thanks again, JP

Note that the proper line reading (as suggested above) still does not 
help if the other program internally buffers IO.

Kind regards

	robert

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