Re: A Bug in History

Haha, apologies. Ignore the above for the moment.

I'm in the process of submitting a bugfix, and I was just testing
bashbug locally with some dummy data, intending to send the email to myself.

Accidentally sent it to you before I was ready.

Actual email coming soon. :)

-Jason

On Fri, Jan 2, 2026 at 3:20 PM <[email protected]> wrote:

> Configuration Information [Automatically generated, do not change]:
> Machine: The Book
> OS: linux-gnu
> Compiler: gcc
> Compilation CFLAGS: -g -O2
> Phonetic CFLAGS: /ˈɡoʊ.to <http://xn--6oa.to>ʊ/
> uname output: Sudocode 1.0.0-aleph-0 λογ-OS ϺΜΠ PREEMPT_DYNAMIC ευ-Fri
> 08:21 ευTC 20XY Bk GNU/Linux
>
> Bash Version: latest
> Patch Level: 0
> Release Status: release
>
> Description:
>
>     Fix interaction between shell history and case-in-comsub
>
>     In interactive mode, the following lines all behave
>     as expected. That is, they do not cause history expansion,
>     and they each execute without printing to stderr.
>
>     1. echo $(if true; then echo 'hi!'; fi)
>     2. echo $(if false; then echo 'hi!'; fi)
>     3. echo "$(if true; then echo 'hi!'; fi)"
>     4. echo "$(if false; then echo 'hi!'; fi)"
>     5. echo $(case a in a) echo 'hi!';; esac)
>     6. echo $(case a in b) echo 'hi!';; esac)
>
>     The same correct (lack of) behavior is observed for all other
>     forms of conditional, whether the condition is true or false,
>     and whether the outer comsub is double quoted or not quoted.
>     (e.g., for, while, until, [[ ]] && { }, [ ] || { }, etc.)
>
>     However, in cases of the following form:
>
>     7. echo "$(case a in a) echo 'hi!';; esac)"
>     8. echo "$(case a in b) echo 'hi!';; esac)"
>
>     we get the following output, even in cases for which the
>     enclosing case pattern is false.
>
>     > bash: !': event not found
>
>     Commands of the above form may print other strings, depending
>     on the contents of the shell's history.
>
>     This commit provides a simple first draft of a fix in subst.c,
>     and adds the file tests/comsub28.sub to verify that history
>     expansion in single quotes no longer occurs in these contexts.
>
>     Limitations:
>     * The current fix does not attempt to address arbitrarily nested
>       case statements inside comsubs. A more complete fix to this
>       problem would be better handled by someone with more familiarity
>       with the codebase (e.g. Chet, if he thinks it's worth the time.)
>     * Another reason for not pursuing a more general fix at the moment
>       is that I'm not sure whether this bug is a symptom of a more
>       general problem in the parser related to case stmts inside comsubs.
>       I mention this only because I fixed a similar bug back in 2020
>       related to SEMI_SEMI_AND inside of case statements within comsubs,
>       which I never got around to submitting and which was eventually
>       fixed. Since this is the second time I've encountered $(case)
>       related bugs, I decided to keep the fix simple for now, since I'm
>       not sure if this fix is just addressing a symptom and not the cause.
>
>     I'm by no means an expert on the code base, so apologies in
>     advance for any glaringly obvious errors or bad decisions.
>
> Repeat-By:
>
>         echo "$(case a in b) echo 'hi!';; esac)"
>
> Fix:
>
>         Current version of the fix uses a simple heuristic check
>         (to see if we're inside a `case` statement) to the function
>         `skip_to_histexp` in the file `subst.c`.
>
>