bug#75308: 30.0.93; man.el assume shell is bash

[Stefan Kangas <stefankangas@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> Cc: Michael Albinus <michael.albinus@gmx.de>
>> From: Stefan Kangas <stefankangas@gmail.com>
>> Date: Fri, 3 Jan 2025 02:46:28 -0600
>>
>> Ted Phelps <phelps@gnusto.com> writes:
>>
>> > Steps to reproduce:
>> > * env SHELL=/bin/tcsh emacs -Q
>> > * invoke M-x man
>> > * request a man page (e.g. emacs)
>> >
>> > This will produce output like the following instead of the man page:
>> >
>> >     Unmatched '''.
>> >     BEGIN: Command not found.
>> >     anonblank=0: Command not found.
>> >     }: Command not found.
>> >     Illegal variable name.
>> >     {: Command not found.
>> >     }: Command not found.
>> >     Illegal variable name.
>> >     Badly placed ()'s.
>> >     Unmatched '''.
>> >
>> >     process exited abnormally with code 1
>> >
>> > Replacing /bin/tcsh with /bin/bash in the above command produces the
>> > expected man page.
>> >
>> > It looks like the behavior was broken by the following commit:
>> >
>> >     commit 861ac933dd8aed1028edc4b9142400e3702874d5
>> >     Author: Michael Albinus <michael.albinus@gmx.de>
>> >     Date:   Wed Nov 1 16:54:31 2023 +0100
>> >
>> > Many thanks,
>> > -Ted
>>
>> Thanks for the bug report.  For emacs-30, we should look into a some
>> small workaround.  I'm copying in Michae.
>
> I think we should force SHELL to be 'sh' (except on Windows) before
> calling shell-command etc.

I was first thinking /bin/bash but if we don't expect to need it, then
sh is better.