Re: Bash heredoc on FD 3

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Jan  8 12:27, Corinna Vinschen wrote:
> On Jan  7 16:19, Steven Penny wrote:
> > On Mon, 7 Jan 2019 20:03:13, Corinna Vinschen wrote:
> > > I can't reproduce this with my latest code.  It works fine for me
> > > every time, independently of POSIXLY_CORRECT.
> > > 
> > > I uploaded new snapshots to https://cygwin.com/snapshots/ with all
> > > the latest changes.  Please try again.
> > 
> > I retested with cygwin1-20190107.dll.xz. My results below. Note that "success"
> > means that with Bash, the script runs without error, regardless of
> > "POSIXLY_CORRECT" variable as you said. "failure" is to mean that with Bash,
> > running with "POSIXLY_CORRECT" produces this error:
> > 
> >    awk: error: can't open source file `/dev/fd/3' for reading (Permission
> >    denied)
> > 
> > Windows 10: success
> > Windows 8.1: failure
> > Windows 7: failure
> > [...]
> 
> I could reproduce this on W8.1.  After some debugging it turned out that
> this is, in fact, not related to POSIXLY_CORRECT at all.
> 
> POSIXLY_CORRECT only changes the way the file is used in gawk.  If
> POSIXLY_CORRECT isn't set, it just uses the incoming file descriptor 3
> due to some code handling the path "/dev/fd/<descriptor>" differently.
> This works fine under all circumstances because it does not trigger my
> new code for /proc/<pid>/fd/<descriptor> at all.
> 
> However, as soon as POSIXLY_CORRECT is set, my new code is triggered and
> falls flat on its face on pre-W10 systems (serves me right for
> developing and testing on W10 only).  The reason is that file delete
> semantics have changed on W10.  On pre-W10, reopening a file by handle
> (equivalent to the Win32 API call ReOpenFile) does not work on files for
> which the delete dispostion has been set.  This works fine on W10,
> though.
> 
> Back to the drawing board.  I have an idea or two how to workaround this
> shortcoming of pre-W10 systems.
> 
> Just FTR, I really like what MSFT changes in W10 under the hood.  I'm
> especially happy that the changes for WSL are exposed to the Windows
> subsystem, too, so we can profit from them as well.  Personally I'm
> not looking back to pre-W10 systems at all.

I added some changes to make this work in older systems as well.
I uploaded new snapshots to //cygwin.com/snapshots/

Please try.


Thanks,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer

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