On 21.11.2006 01:21, Vidar Hokstad wrote:
> Antonio Moreno wrote:
>> Robert Klemme wrote:
>>> On 20.11.2006 20:24, Antonio Moreno wrote:
>>>> I'm trying to code a script for replacing an application which takes
>>>> it's input from file descriptors 0 (stdin) and 1 (stdout).
>>> This is not possible.  You can only read from stdin and not stdout.
>>>
>> (snif)
> 
> 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.

Thanks for elaborating!  Actually I was not aware that you can do this. 
  However, even if it is possible I would not do it as the general 
convention is that 1 should be written to and 0 be read from only. 
After all, what do you gain by reading from FD 1 if nothing writes to 
it? :-)

But, as we have seen, the issue at hand was about connecting parent and 
child process through pipes.

Kind regards

	robert