Re: fg via keybind modifies tty settings

[Chet Ramey]

On 9/20/24 7:23 PM, David Moberg wrote:

> Bash Version: 5.2
> Patch Level: 21
> Release Status: release
>
> Description:
>          When a process/job is suspended, foregrounded via ctrl-a as a
> keybinding for fg, and then
>          suspended again, the tty will be in a surprising state where no
> input is seen (-echo)

When the shell starts a job with `fg', it fetches the tty settings so it
can restore them if the job exits or stops due to a signal. That way, a
job that modifies the terminal settings, then crashes, doesn't leave the
terminal in an unusable state.

When you run a command from a readline key binding, it still runs in the
context of readline obtaining a line from the keyboard -- it's just another
key binding, like C-f. Readline doesn't reset the tty settings to run the
binding, and bash doesn't reset them to run the command.

When `fg' runs and starts the job, the shell fetches the tty settings as
usual, but they are the tty settings readline uses when it's reading input.
It assumes those are the `normal' settings.

When vim stops due to the SIGTSTP, the shell restores what it thinks are
the normal tty settings -- the ones it fetched after readline modified
them. The difference you see between the `working' and `broken' settings
is what readline does so it can read input.

I will see if this can be changed by having `fg' detect whether it's
being run from a key binding and not fetch the terminal settings in that
case.

Chet

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/