From: Michal Suchanek <hramrach@...>
Date: 2011-05-17T00:29:48+09:00
Subject: Re: Shell pipeline in Ruby?

On 12 May 2011 18:05, Michal Suchanek <hramrach@centrum.cz> wrote:
> Hello,
>
> how do you write an equivalent of
>
> $ cmdA | cmdB | cmdC
>
> in Ruby?
>
> Specifically, I would like to see the PID, return value and stderr of
> each of these commands but I would like cmdB to read the stdout of
> cmdA directly, on its stdin, and similarily for cmdC and cmdB.
>
> Here I am not interested in feeding cmdA some particular input (eg. it
> can read /dev/null for all I care) but in general gluing arbitrary fd
> to its stdin might be desirable in other cases.
>

Thanks for all the replies.

To sum up there are multiple methods to achieve this.

 - fork - works on ruby 1.8 but not on Windows
 - Open3  - very nice interface with pipeline_start and such which
does much of the setup behind the scenes but from what I read on the
Net does not work on Windows, again
 - Open3-win32 and Open4 exist to address this issue but they may not
have the same interface.
 - Process.spawn - works only in ruby 1.9 but should be portable to
Windows should you need it. Basically equivalent to Open3 except you
see all the gory details. Not sure why Open3 does not use this on
Windows. Maybe Open3 was in 1.8 already when spawn did not allow for
redirects or something.
 - Shell - somewhat not well known and not well documented Ruby
library. You will reimplement this if you use one of the above ;-)

For reading and writing numerous pipes you can use either a Ruby
thread per pipe or a select loop, either works.

Thanks

Michal