From: Antonio Moreno <ejsglobal@...>
Date: 2006-11-22T00:13:51+09:00
Subject: Re: File descriptors

Vidar Hokstad wrote:
>
> 
> Robert is half right and half wrong (on POSIX compatible platforms
> anyway):
> 
> readable_fd1 = IO.for_fd(1,"r")
> STDERR.puts "FROM STDIN  (fd 0): #{STDIN.read}"
> STDERR.puts "FROM STDOUT (fd 1): #{readable_fd1.read}"
> 
> You might argue that if someone provides a file on fd 1 it isn't really
> stdout, but you can certainly open fd 1 (or any fd) both for reading or
> writing if whatever is attached to them supports the mode you want - fd
> 0, 1 and 2 aren't special in any way to the OS.
> 
> You can test the above like this:
>   ruby in.rb 1<bar.txt 0<foo.txt
> 
> The 1<filename and 0<filename opens the files for input at the file
> descriptors specified.
> 
> Vidar

Thanks, Vidar! You solved half my problem. Now all I'd need to know is 
how to write on fd 1 of a process spawned from ruby with IO.popen.

I tried the following without success:

f = open("|-", "w+")
if f == nil
     puts "This is Child"
     r_fd1 = IO.for_fd(1,"r+")
     STDERR.puts "FROM STDOUT (fd 1): #{r_fd1.read}"
     STDERR.puts "Hijo: #{STDIN.gets}"
     exit 69
else
     STDERR.puts "Running parent."
     f.puts "From parent\n"
     STDERR.puts "Got: #{f.gets}"
     STDIN.puts "To fd 1 of the child."
     pid = Process.wait
     STDERR.puts "Child terminated, pid = #{pid}, exit code = #{$? >> 
8}"
end

If I commmented the lines with "readable_fd1", this piece of code would 
run. What I get is:

fork.rb:4:in `for_fd': Invalid argument (Errno::EINVAL)
        from fork.rb:4
Running parent.
fork.rb:10:in `write': Broken pipe (Errno::EPIPE)
        from fork.rb:10



Thanks again.

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