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Re: redraw-current-line fails with multiline prompts


From: Hugh Davenport
Subject: Re: redraw-current-line fails with multiline prompts
Date: Mon, 15 Feb 2016 20:57:31 +0000

February 16 2016 9:11 AM, "Chet Ramey" <address@hidden> wrote:
> 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().

Hey Chet,

Thanks for your reply. OK, so my patch doesn't need that weird for loop.
I couldn't find the redraw_prompt_last_line function when I had a quick
search.

Would that change be something that you would do to replace the readline
function binding redraw_current_line, or would it be something else that
would be exposed? It would be great if there was a way to redraw the prompt
without it generating a lot of extra vertical lines.

Cheers,

Hugh
> 
> 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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