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Subject:	Re: [ANNOUNCEMENT] cygwin 3.1.0-0.6 (TEST)
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Cc:	Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
From:	Michael Haubenwallner <michael DOT haubenwallner AT ssi-schaefer DOT com>
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Date:	Mon, 14 Oct 2019 13:07:22 +0200
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On 10/11/19 11:24 AM, Takashi Yano wrote:
> Hi Michael,
> 
> On Thu, 10 Oct 2019 12:43:56 +0200
> Michael Haubenwallner wrote:
>> I'm encountering another strange behaviour I do not remember to have seen before:
>>
>> Using ssh from some Linux xterm into the Cygwin sshd running on Server 2019
>> does clear the current terminal content as if /usr/bin/clear was executed.
> 
> This is intentional behaviour.
> 
> The pseudo console has its own screen buffer behind, and redraws
> the screen based on the screen buffer at undetermined timing.> The screen buffer is empty at the beginning, so the screen should
> be cleared at the opening of the pty so that the real screen and
> the screen buffer are synchronozed.
> 
> The clear screen is prevented when TERM=dumb, so you can see what
> happens if clear screen is not done by following steps.> 
> 1)  Execute ls or ps to draw something to screen.
> 2) env TERM=dumb ssh <cygwin-hostname>
> 3) Execute cmd.exe.

Well... even that one is counter intuitive regarding the 'Last login' line.
After login into Cygwin sshd, the 'Last login' line is not shown:

haubi AT linuxbox ~ $ ssh cygwin2019
----------------------------------------
> 
> haubi AT cygwin2019 ~
> $
> 
> 
> 
> 
> 
> 
> 
----------------------------------------

When starting cmd, the terminal does loose colors, and the 'Last login'
line suddenly is shown as first line:
----------------------------------------
> Last login: Mon Oct 14 12:30:52 2019 from 192.168.56.1
> 
> haubi AT cygwin2019 ~
> $ cmd
> Microsoft Windows [Version 10.0.17763.805]
> (c) 2018 Microsoft Corporation. All rights reserved.
> 
> C:\cygwin64\home\haubi> 
> 
> 
----------------------------------------

However, with TERM=dumb, the terminal content is:
----------------------------------------
> {some output from previous linux commands}
> {some output}
> {some output}
> {some output}
> {some output}
> haubi AT linuxbox ~ $ TERM=dumb ssh cygwin2019
> Last login: Mon Oct 14 12:37:24 2019 from 192.168.56.1
> 
> haubi AT cygwin2019 ~
> $ 
----------------------------------------

And when cmd was started:
----------------------------------------
> Last login: Mon Oct 14 12:37:24 2019 from 192.168.56.1
> 
> haubi AT cygwin2019 ~
> $ cmd
> Microsoft Windows [Version 10.0.17763.805]
> (c) 2018 Microsoft Corporation. All rights reserved.
> 
> C:\cygwin64\home\haubi>
> 
> 
----------------------------------------

Actually I do prefer the TERM=dumb behaviour, having the current terminal
buffer content get redrawn at line 1 when cmd is started only, not when
running just Cygwin programs.

My real problem is more sophisticated, and boils down to the creation of some
pty's in a row, each having some commands run inside, and I do expect to see
the output of each command while the series runs and when done, much like:

----------------------------------------
> {some output from previous linux commands}
> {some output}
> {some output}
> haubi AT linuxbox ~ $ ssh -t cygwin2016 hostname; hostname; ssh -t cygwin2016 hostname
> cygwin2016
> Connection to cygwin2016 closed.
> linuxbox
> cygwin2016
> Connection to cygwin2016 closed.
> haubi AT linuxbox ~ $
----------------------------------------

And looking at the code actually makes me belive that even emacs does have
troubles when the clear screen code is emitted on pty creation...

Thanks!
/haubi/ (in hope that "embedding the screen shots" does work)

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