From: Jason Roelofs <jameskilton@...>
Date: 2007-08-03T01:46:43+09:00
Subject: Re: Piping two shell commands together

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`#{cmd1.join(' ')} | #{cmd2.join(' ')}`

Those are backticks. Let the system handle piping with the '|' character.

Jason

On 8/2/07, Hans Fugal <fugalh@zianet.com> wrote:
>
> I want to pipe two system commands together from within ruby. cmd1 and
> cmd2 are arrays, e.g.
>
> cmd1 = ['oggdec','-o','-',oldpath]
> cmd2 = ['lame','-',newpath]
>
> I think I can do the following,
>
> IO.popen('-','r') do |p1|
>    exec cmd1 unless p1
>    IO.popen('-','w') do |p2|
>      exec cmd2 unless p2
>      p2.write(p1.read)
>    end
> end
>
> but I don't like the line "p2.write(p1.read)", because I think it will
> read into memory from p1 before turning around and writing it to p2.
> This may work for the above example, but it's not very pipelike and I
> worry that read might return early (I'm not sure what the semantics of
> that are in Ruby, but in C I'd have to account for that).
>
> Plus I don't like the popen '-'/exec combination. I'd love a more
> elgant, efficient, and/or safer idiom if anyone can think of one.
>
>

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