From: Robert Klemme <shortcutter@...>
Date: 2011-05-13T23:23:15+09:00
Subject: Re: Shell pipeline in Ruby?

On Fri, May 13, 2011 at 3:27 PM, Michal Suchanek <hramrach@centrum.cz> wrote:
> On 13 May 2011 10:44, Robert Klemme <shortcutter@googlemail.com> wrote:
>> On Thu, May 12, 2011 at 6:05 PM, Michal Suchanek <hramrach@centrum.cz> wrote:
>>> 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.
>>
>> $ ri Open3.pipeline_r Open3.pipeline_start
>>
> Again, like in Open3.pipeline the :err argument used in the example is
> not documented.

Not true.  From ri Open3.pipeline_r in 1.9.2p180:

Each cmd is a string or an array. If it is an array, the elements are passed
to Process.spawn.

  cmd:
    commandline                              command line string which
is passed to a shell
    [env, commandline, opts]                 command line string which
is passed to a shell
    [env, cmdname, arg1, ..., opts]          command name and one or
more arguments (no shell)
    [env, [cmdname, argv0], arg1, ..., opts] command name and
arguments including argv[0] (no shell)

  Note that env and opts are optional, as Process.spawn.

Then

$ ri Process.spawn

> From the description of the example it seems it captures the stderr of
> all the commands together.
>
> Are there more arguments like that?
>
> What do they mean?

See above.

> Also this is available in ruby 1.9 only.

Well?

Cheers

robert

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