zpty -r and pipes

zpty -r and pipes

[Stephane Chazelas]

$ zsh -c 'zmodload zsh/zpty; zpty E echo test; zpty -r E'
test

But if I pipe it to anything:

$ zsh -c 'zmodload zsh/zpty; zpty E echo test; zpty -r E | cat'
$

No output.

Those are fine though:

$ zsh -c 'zmodload zsh/zpty; zpty E echo test; echo $(zpty -r E)'
test
$ zsh -c 'zmodload zsh/zpty; zpty E echo test; {zpty -r E} | cat'
test


Sounds like some bug in fd management.

$ zsh --version
zsh 5.0.2 (x86_64-unknown-linux-gnu)

-- 
Stephane

Re: zpty -r and pipes

[Peter Stephenson]

On Mon, 13 May 2013 16:27:20 +0100
Stephane Chazelas <stephane.chazelas@gmail.com> wrote:
> $ zsh -c 'zmodload zsh/zpty; zpty E echo test; zpty -r E'
> test
> 
> But if I pipe it to anything:
> 
> $ zsh -c 'zmodload zsh/zpty; zpty E echo test; zpty -r E | cat'
> $
> 
> No output.
> 
> Those are fine though:
> 
> $ zsh -c 'zmodload zsh/zpty; zpty E echo test; echo $(zpty -r E)'
> test
> $ zsh -c 'zmodload zsh/zpty; zpty E echo test; {zpty -r E} | cat'
> test

First guess and without looking into it is it might be a job control
thing.  Those look just the circumstances where we wouldn't have a
special job in a subshell (pipeline) or where we would (command
substitution, new current-shell process before the fork).

But I could just be wasting typing time.

Not sure what this has got to do with file descriptors anyway.

pws

Re: zpty -r and pipes

[Bart Schaefer]

On Mon, May 13, 2013 at 8:27 AM, Stephane Chazelas
<stephane.chazelas@gmail.com> wrote:
>
> $ zsh -c 'zmodload zsh/zpty; zpty E echo test; zpty -r E | cat'
> $
>
> No output.

Check the exit status:

% zsh -c 'zmodload zsh/zpty; zpty E echo test; zpty -r E | cat &&
print $pipestatus'
1 0
%

"zpty -r" is failing.  I wonder if this is another case of a read()
being interrupted by a signal?  It seems to be a race, I can affect it
by inserting a sleep:

% zsh -c 'zmodload zsh/zpty; zpty E echo test; (zpty -r E) | cat'
test
% zsh -c 'zmodload zsh/zpty; zpty E echo test; {sleep 1; zpty -r E} | cat'
% zsh -c 'zmodload zsh/zpty; zpty E echo test; {zpty -r E; sleep 1} | cat'
test