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From: Clark Wang <dearvoid@gmail.com>
Newsgroups: gnu.bash.bug
Subject: Re: Forgets color when resizing with newline in prompt
Date: Tue, 8 Oct 2019 18:38:04 +0800
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Approved: bug-bash@gnu.org
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References: <E1iGmBV-0005KB-62@jcn> <CADv8-oi9Sac8kHCy9xK7bCBHeu2tai5AMzmt8NT9BbweTMDnMQ@mail.gmail.com>
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To: ao2 <ao2@jcn.localdomain>
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On Sun, Oct 6, 2019 at 12:17 AM ao2 <ao2@jcn.localdomain> wrote:

> [...]
>
> Description:
>
>         I noticed that when there is a newline in the prompt bash "forgets"
>         about ANSI color sequences when the window is resized. I am not
> sure
>         f this is general for other kinds of ANSI escape codes.
>
> Repeat-By:
>
>         1. Set the prompt to something like:
>
>              PS1='\[\033[36m\]cyan\ncyan\[\033[0m\]\$ '
>
>            or equivalently to:
>
>              PS1='\[$(tput setaf 6)\]cyan\ncyan\[$(tput sgr0)\]\$ '
>
>         2. Resize the terminal window and see the second line of the prompt
>            loosing the color.
>

Did a strace when resizing the tty and it outputs this:

    ioctl(0, TIOCGWINSZ, {ws_row=73, ws_col=228, ws_xpixel=0, ws_ypixel=0})
= 0
    write(2, "\r\33[Kcyan\33[m\17# ", 14)   = 14

So it seems like Bash only reprint the last line of the prompt string when
SIGWINCH is received.

    \r -- move cursor to the beginning of current line
    \33[K -- clear from cursor to the end of the line
<https://en.wikipedia.org/wiki/ANSI_escape_code>

I don't think this is a bug and your workaround should be the best
practice. :)

-clark