Re: [ptxdist] Backspace not working in terminal (using ssh)

[Ian Abbott <abbotti@mev.co.uk>]

On 21/03/2019 13:33, Michael Olbrich wrote:
> On Thu, Mar 21, 2019 at 12:46:40PM +0000, Ian Abbott wrote:
>> On 20/03/2019 15:41, Michael Olbrich wrote:
>>> On Wed, Mar 20, 2019 at 12:41:47PM +0000, Ian Abbott wrote:
>>>> On 20/03/2019 09:15, Dold, Wolfram wrote:
>>>>> On Tue, 2019-03-19 at 17:42 +0000, Ian Abbott wrote:
>>>>>> On 19/03/2019 12:33, Dold, Wolfram wrote:
>>>>>>> Hi Ian,
>>>>>>> On Tue, 2019-03-19 at 12:06 +0000, Ian Abbott wrote:
>>>>>>>> On 19/03/2019 09:17, Dold, Wolfram wrote:
>>>>>>>>> Hi there,
>>>>>>>>> when we connect via ssh to our embedded device, the backspace key does not work.
>>>>>>>>> During the analysis we found out that the passage
>>>>>>>>>
>>>>>>>>> # This fixes the backspace when telnetting in.
>>>>>>>>> if [ "$TERM" != "linux" ]; then
>>>>>>>>>              stty erase ^H
>>>>>>>>> fi
>>>>>>>>>
>>>>>>>>> from the file '/etc/profile' contained in ptxdist.
>>>>>>>>>
>>>>>>>>> Now I want to ask, how best to fix this behavior?
>>>>>>>>> Can the passage simply be omitted? (At least the comment lets me assume that, because there 'telnet' is
>>>>>>>>> mentioned
>>>>>>>>> and
>>>>>>>>> that is no longer necessarily state of the art).
>>>>>>>>> Or does omitting it lead to other unwanted side effects?
>>>>>>>>>
>>>>>>>>> Any help would be appreciated.
>> [snip because it's getting a bit long]
>>
>>>> I've no idea why that bit of the /etc/profile file is there, but I guess it
>>>> must have suited one of the PTXdist developers at the time.  A "git blame"
>>>> only revealed that the whole file was added in 2006, so I don't know how
>>>> relevant that part of it is today.
>>>
>>> This code was moved around some more. It was actually introduced in the
>>> initial import from CVS in 2003 :-). Telnet works just fine without this,
>>> so I guess this is no longer needed.
>>
>> Perhaps it was there for the Windows Telnet client which seems to send ASCII
>> BS when the "Backspace" key is pressed and ASCII DEL when the (less
>> conveniently placed) "Delete" key is pressed.  This mimics the codes sent by
>> the VT-102 "Backspace" and "Delete" keys which were both conveniently
>> placed.
>>
>> The Windows telnet client has a -t option to set the terminal type to one of
>> "vt100", "vt52", "ansi", or "vtnt", but it doesn't pass the selected
>> terminal type to the server, and this doesn't seem to have any effect on the
>> codes sent by the "Backspace" and "Delete" keys.  The TERM environment
>> variable ends up getting set to "vt102" by default on my PTXdist systems if
>> a terminal type hasn't been passed through by the Telnet client.  I don't
>> know if that is configurable.
>>
>> The Windows Telnet client isn't installed by default, but can still be
>> installed as a "Windows Feature".  I guess most people who used it would
>> have switched to something like PuTTY by now.
> 
> I'm pretty sure it was a Linux issue. I remember having problems like this
> a long time ago.

I guess it used to do `stty erase ^H` always and an exception was added 
later for terminal type "linux".  The Linux vt console sends ASCII DEL 
for the Backspace key, and ASCII ESC [ 3 ~ for the Delete key, so that 
seems like it was a reasonably cautious change at the time.

>>> I'll be happy to apply a patch that removes this.
>>
>> I'm worried that doing so might annoy some people who expect the existing
>> behavior.
> 
> I'd rather fix a real problem. If it causes issues, then we'll try to find
> a solution.

I suppose using the GNU coreutils default value for the stty erase 
character ( ^? (ASCII DEL) by default) is likely to cause the least 
problems overall.  This also seems to be the default for FreeBSD 
(although FreeBSD stty also has an "erase2" option set to ^H (ASCII BS) 
by default).

-- 
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