Focal: strange behavior of the prompt for the tcsh shell

[Tom H]

On Mon, Sep 21, 2020 at 9:25 AM Uwe Brauer <oub at mat.ucm.es> wrote:
>
> I am running a Thinkpad X1, and upgraded from 16.04 to 20.04.
>
> I always use the tcsh shell, with the following setting
> set prompt   = '%B%n@%m:%~\n%T %#%b'
>
> That worked perfectly since 16.04
>
> However now when repeat a command with left arrow up and then
> use the right and left arrow keys of my keyboard the cursor
> jumps the line and make it hard to modify the last command.

I installed tcsh, used your prompt above, and experiemced the same
jumping when using my arrow keys.

When I modify your prompt to either
set prompt   = '%n@%m:%~\n%T %# '
or
set prompt   = '%B%n@%m:%~ @%T %#%b '
the jumping stops.

There must be some bad interaction between "%B...%b" and "\n".

There was an upgrade from 6.20 to 6.21 on July 16th 2019 that fixed
Debian bug 888479 and its title is "tcsh 6.20.00-7 crashes when
entering non-ascii characters." Maybe your problem's a side-effect of
that bug fix. Maybe...