Mail Archives: cygwin/2011/10/08/17:39:56
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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
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#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
int
main()
{
char *argv[4];
char buf;
int fd[2];
int nullfd = open ("/dev/null", O_RDONLY);
pid_t pid;
argv[0] = "bash";
argv[1] = "-ic";
argv[2] = "ls";
argv[3] = '\0';
pipe (fd);
pid = fork();
if (pid == 0)
{
setsid ();
close (0);
close (1);
close (2);
dup2 (nullfd, 0);
dup2 (fd[1], 1);
dup2 (fd[1], 2);
close (fd[1]);
close (nullfd);
execvp (argv[0], argv);
}
close (fd[1]);
close (nullfd);
while (read (fd[0], &buf, 1) > 0)
write (1, &buf, 1);
close (fd[0]);
}
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