Problem redirecting stderr to pipe in subprocess

[Ken Brown]

On 10/8/2011 11:35 AM, Ken Brown wrote:
> The attached STC arose from my attempt to understand the problem
> discussed starting in
>
> http://cygwin.com/ml/cygwin/2011-09/msg00405.html .
>
> I'm starting a new thread because there appears to be a Cygwin problem
> having nothing to do with emacs.
>
> The STC creates a pipe and then runs `bash -ic ls' in a subprocess, with
> both stdout and stderr sent to the pipe. The parent process reads from
> the pipe and echoes it to the terminal.
>
> On Linux, I first get the error messages (presumably expected)
>
> bash: cannot set terminal process group (-1): Invalid argument
> bash: no job control in this shell
>
> followed by the directory listing. On Cygwin, the bash process produces
> no output but is simply stopped, and I have to kill it from another
> terminal before the main program will exit. This happens both with
> cygwin-1.7.9 and the latest snapshot. Here are a few comments:
>
> 1. The problem disappears if I don't send bash's stderr to the pipe.
>
> 2. The problem also disappears if I replace -ic by -c in the call to
> bash, presumably because there's nothing sent to stderr in that case.
>
> 3. The problem disappears if I don't use a pipe but just have the bash
> subprocess write to the terminal, even if I redirect bash's stderr to
> stdout.

Attached is a slight modification of the STC, in which I set stdin for 
the bash subprocess to /dev/null.  With this modification, the program 
works as expected (and as on Linux) with cygwin-1.7.9, but the same 
problem as before occurs with the latest snapshot.

Ken

-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: bash-ls1.c
URL: <http://cygwin.com/pipermail/cygwin/attachments/20111008/0faa47ae/attachment.c>
-------------- next part --------------
--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple