Re: tmux uses ^? for backspace

[Thomas Dickey]

On Mon, Sep 21, 2020 at 09:06:12PM +0200, Přemysl Eric Janouch wrote:
> Hi,
> 
> I've noticed that tmux's kbs/key_backspace entry is inherited from
> "screen", which lists it as ^H, however the default in tmux is \177/^?, see:

generally agreeing that it wouldn't hurt (much) to make kbs=^?

However, keep in mind that tmux is a BSD application (OpenBSD),
which makes the stty erase default to ^H (so changing this
would move the problem around -- perhaps not an improvement).
 
> https://github.com/tmux/tmux/blob/655134f77c927f248f180a7f65c658359e10516e/options-table.c#L184
> https://github.com/tmux/tmux/blob/a5f99e14c6f264e568b860692b89d11f5298a3f2/CHANGES#L382

That's from this commit:

commit 08b07b1a08ad02f7a195437deead0a60f971e1ee
Author: nicm <nicm>
Date:   Thu Nov 14 07:55:01 2019 +0000

    Add an option to set the key sent by backspace for those whose system
    uses ^H rather than ^?. GitHub issue 1969.

which refers to

https://github.com/tmux/tmux/issues/1969
"Leave VERASE setting at the user's preference"

tmux doesn't actually use kbs, as noted in tty-keys.c:

        /* 
         * Check for backspace key using termios VERASE - the terminfo 
         * kbs entry is extremely unreliable, so cannot be safely 
         * used. termios should have a better idea. 
         */
        bspace = tty->tio.c_cc[VERASE];
        if (bspace != _POSIX_VDISABLE && (key & KEYC_MASK_KEY) == bspace)
                key = (key & KEYC_MASK_MODIFIERS)|KEYC_BSPACE;

(n)curses has something similar with the erasechar/erasewchar functions.
But most applications (I think) use some combination of tests for

        KEY_BACKSPACE
        KEY_DC
        '\b'
        '\177'

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net
ftp://ftp.invisible-island.net

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