Redirecting stderr to stdout through pipe doesn't work the way it does in Linux

David Karr
Wed Dec 5 15:11:00 GMT 2018

On Tue, Dec 4, 2018 at 12:52 PM Marco Atzeri <> wrote:

> Am 04.12.2018 um 21:41 schrieb David Karr:
> > "CYGWIN_NT-6.1 WACDTL03DK068X 2.9.0(0.318/5/3)"
> >
> > I installed a version of "kubectl" for windows, and I use it extensively
> in
> > Cygwin bash for scripting command-line automation. In general, this works
> > perfectly fine. I even use the same scripting in a Linux VM.
> >
> > I'm seeing an issue with one script that works fine in the Linux VM, but
> > not in Cygwin.
> >
> > The command line is approximately this:
> >
> >       kubectl exec pod -c container -i -t -- grep "string"
> > 2>&1 | sed -e 's/^propname=//'
> >
> > In Linux, this works perfectly fine.  In Cygwin, it says "stdout is not a
> > tty".
> >
> > I haven't updated my local Cygwin installation for quite a while. I'd
> > prefer not to, unless there is a strong chance this kind of thing would
> be
> > fixed.
> >
> as kubectl is not a Cygwin program, it is not aware of cygwin pty.
> You can try to use winpty to overcome the problem.
It turns out that not only had I already used winpty for similar
functionality, it was actually in place in the pipeline when I tried to do
this.  When I turned on debugging output, it showed that kubectl was
already being wrapped by winpty when it reported "stdout is not a tty".
However, this was one shell script wrapper deeper than I usually call it.
Does it matter whether winpty is called from the shell script I'm calling,
or from the script being called by the script I'm calling?

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