From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-10-14T01:21:55+09:00
Subject: Re: exec and pipe

On Fri, 14 Oct 2005, ientu wrote:

> I think IO.popen waits for  the process to terminate before putting any
> data into the pipe. This doesn't work for me, as I have to process the
> output in real time.

that's what popen is for:

   harp:~ > cat a.rb
   STDOUT.sync = true and loop{ sleep 0.42 and puts Time::now }

   harp:~ > cat b.rb
   IO::popen('ruby a.rb'){|pipe| loop{ print pipe.gets }}

   harp:~ > ruby b.rb
   Thu Oct 13 09:58:03 MDT 2005
   Thu Oct 13 09:58:03 MDT 2005
   Thu Oct 13 09:58:04 MDT 2005
   Thu Oct 13 09:58:04 MDT 2005
   Thu Oct 13 09:58:04 MDT 2005
   Thu Oct 13 09:58:05 MDT 2005
   Thu Oct 13 09:58:05 MDT 2005
   Thu Oct 13 09:58:06 MDT 2005
   Thu Oct 13 09:58:06 MDT 2005
   Thu Oct 13 09:58:07 MDT 2005
   Thu Oct 13 09:58:07 MDT 2005
   Thu Oct 13 09:58:07 MDT 2005
   Thu Oct 13 09:58:08 MDT 2005
   Thu Oct 13 09:58:08 MDT 2005
   Thu Oct 13 09:58:09 MDT 2005
   ...
   ...
   ...

perhaps your perl code is buffering output.  make sure the stdout of the perl
process is not fully buffered.  programs are, by default, fully buffered when
run into a pipe.


you can 'fix' broken code by creating a wrapper that does

   #! /usr/bin/env ruby
   STDOUT.sync = true
   exec(ARGV.join(' '))

and running all code, including perl code, under this wrapper.  so

   IO::popen('wrapper a.pl'){|pipe| loop{ print pipe.gets }}


hth.

-a
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