Re: Bash spews bracketed-paste escape sequences when handling signal.

[Chet Ramey]

On 12/15/24 2:16 AM, Kaz Kylheku wrote:

> > > If you do not have "trap : ALRM" then this doesn't happen.
> >
> > Because SIGALRM is a terminating signal that kills the shell.
>
> But no; I mean the shell keeps running in that case. Try it:
>
>    $ kill -ALRM $$
>    $ # didn't die

Then something about the execution environment is weird. On a clean shell:

$ echo $BASH_VERSION
5.3.0(1)-beta
$ echo $$
28545
$ kill -ALRM $$
Alarm clock: 14

[shell terminates]. Thisa is also on macOS. The most likely cause is that
you're ignoring SIGALRM, and it was ignored when the shell started.


> Furthermore, if the Bash trap for ALRM is not installed, then
> the readline behavior in question (emission of terminal sequences)
> doesn't occur.

More evidence that the signal is ignored; readline doesn't install a
handler if the calling application has the signal ignored.

> Since "trap : ALRM" is a Bash feature and not a readline feature,
> it's hard to escape the conclusion that Bash is somehow acting as an
> enabler for the behavior.
>
> The right fix may be to stay away from SIGALRM, since readline
> clearly uses it for something.

It uses SIGALRM for timeouts if select/pselect are unavailable, but not
otherwise. However, since it's a fatal signal that applications commonly
use, readline catches it and cleans up the terminal.

> Disabling bracketed paste is probably a bad workaround; what if
> some Basta user wants that to work?

I meant as an individual choice.

> With signals other than SIGALRM, the code has to be careful; if it
> ever happens that the signal is delivered without the trap being
> in place, Bash will die.

Same with SIGALRM, too.


--
``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/