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Re: redraw-current-line fails with multiline prompts


From: Chet Ramey
Subject: Re: redraw-current-line fails with multiline prompts
Date: Mon, 15 Feb 2016 15:10:10 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.5.1

On 2/12/16 12:45 AM, Hugh Davenport wrote:

> Bash Version: 4.3
> Patch Level: 30
> Release Status: release
> 
> Description:
>       Assume I have a multiline prompt (`PS1="first\nsecond"`), and a bind to
>       redraw-current-line (`bind '"\er": redraw-current-line'`). When I
>       refresh the line with M-r, I get the following output:
>       first
>       first
>       second
> 
>       What is happening is that the redraw-current-line is assuming that I
>       only have a single line prompt, and is just redrawing that current
>       line. Two possible solutions to this are:
>         1) Work out the last line of the prompt and only redraw that (makes
>               sense with function name, or
>         2) Work out number of lines in the prompt, and redraw entire prompt.
> 
> Repeat-By:
>       Have a rc file with the following
>       PS1="first\nsecond"
>       bind '"\er": redraw-current-line'
> 
>       Then start bash with that rc file, and hit M-r a few times, notice that
>       the last line gets overwritten, but the first line doesn't. You can
>       expand this by having PS="first\nsecond\nthird" and seeing that the
>       third line gets overwritten, but not the first and the second. This
>       leads to a lot of wasted vertical space if you are redrawing often.
> 
> Fix:
>       I've got a patch for option 2, which works well with existing methods,
>       but makes the function name a bit misleading.

Thanks for the report.  It's sufficient to change the call from
rl_forced_update_display to rl_redraw_prompt_last_line (your option 1).
This is what bash does for bash_execute_unix_command().

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/



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