Thanks for the clarification Chet.

I tried the same test with dash, on the same terminal. It does not have this issue. I understand dash doesn't use readline and has less features. Still, with PS1 set the same it does not have this prompt issue -- how can it know the correct physical cursor position but readline can't?

And going back to older bash 4.4 (and related readline version) I can't reproduce the issue. I'll retest once the patch is in stable and try to figure out better. I'll make a new issue if it's reproducible.

@chet: I spotted the patch you did for this issue. I'm running the bash-devel-git version now (which I confirmed has this patch).

On Gnome Terminal (and other VTE based terminals) the issue is much improved with the patch!

• If windows are resized slowly the issue no longer happens.
• If windows are resized faster it still happens that the prompt is not fully erased before printing it anew. But afterwards, if the window is resized to be wider than the prompt it clears the entire (faulty) prompt.
• I've captured a video to show the difference (resizing slowly vs resizing faster): https://i.imgur.com/CfVCbQy.mp4
• And if the window is resized multiple times very quickly while it is smaller than the prompt, the entire terminal window can fill up with the prompt: https://i.imgur.com/Gr8HHDy.png

While with bash 5.1.8 I also have this issue on Alacritty, with the patch I can no longer reproduce it on Alacritty. Alacritty is GPU accelerated, Gnome Terminal isn't. Maybe that is what makes the difference.

@domson: thanks, I haven't gotten round to it yet. I'll try it next to see if the workaround also has this difference between Alacritty and Gnome Terminal.

Readline redisplay after a SIGWINCH doesn't try to alter anything but the last line of the line its displaying, since you can never tell what terminal emulators will do with wrapping or rewrapping text on the rest of the display.

Readline keeps an array of prompt string offsets where it has to wrap the prompt to a new screen line. What's clear is that this needs to be updated upon receipt of a SIGWINCH if the screen width is less than the visible prompt length.

Without doing that, redisplay is going to lose track of where it is on the screen and eventually garble the display. For instance, it will eventually think it's in column 0 when the terminal emulator has wrapped the screen and it's on, say, column 35, assume that it does not need to clear the line, and reprint the prompt.

Readline only prints the prompt once -- if it thinks it's in column 0 and doesn't clear the line, it will appear that it's printing the prompt multiple times, but that's not what happens.

Okay, did that. And added `-lreadline` to solve some other error it gave. Now it complains about missing `main`. I don't what to do with examples/loadables/Makefile, or how to get from it what I need to add to gcc command. Final clue?

$ gcc -lreadline -I/usr/include/bash/ -I/usr/include/bash/include/ -I/usr/include/bash/builtins/ -Ibash/lib -o reprompt reprompt.c
/usr/bin/ld: /usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/../../../../lib/Scrt1.o: in function `_start':
(.text+0x24): undefined reference to `main'
collect2: error: ld returned 1 exit status

you need to `git clone https://git.savannah.gnu.org/git/bash.git` and include its lib directory.

you're welcome.

Actually IMHO I think that the terminal emulator application should take care of this to keep responsibility transparent and clear :-)

sorry about the PROMPT_COMMAND. I use it to dynamically shorten the PS1 (e.g strip user name, shorten current dir, shorten git helper etc.) for very tiny windows on window resize. it works pretty well with the described technique.

# You can control this behavior as needed with

function Terminal::ps () {
  .. your custom prompt line according to window size ...
}

declare PROMPT_COMMAND='Terminal::ps'

# for dynamic line wrap on window change you also need a custom loadable builtin named 'reprompt'  I wrote. I add its source as attachment. you can build it like the example custom builtins in bash source.

enable -f "/path/to/reprompt" reprompt
trap '$PROMPT_COMMAND; reprompt "$PS1"; ' SIGWINCH

# reprompt just resets/clears the current line, nothing else.


(file #51958)