Re: ob-shell: proposal to remove "posh"

[Ihor Radchenko]

Matt <matt@excalamus.com> writes:

> There was discussion about different shells, Eric asked for others, "posh" 
> was mentioned as "specially for POSIX compatibility checks", and then a 
> "posh" was added to ob-shell.el by Eric (fb09863f).
> https://git.savannah.gnu.org/cgit/emacs/org-mode.git/commit/?id=fb09863fbb35bf15bcf78262b6e31b8b8b8617e7
>
> Around that time are a few stack exchange answers suggesting to use posh, the 
> "Policy-compliant Ordinary SHell", to test for posix compliance.  Debian 
> distributed it by saying, "using posh as your /bin/sh may reveal breakage."  
> It seems that posh was used to check for POSIX compliance.  It's still 
> available on Debian.
> https://unix.stackexchange.com/questions/48786/how-can-i-test-for-posix-compliance-of-shell-scripts
> https://web.archive.org/web/20130930231522/https://packages.debian.org/sid/posh
> https://packages.debian.org/sid/posh

It is also still available on Gentoo.

> ** No one uses the "Policy-compliant Ordinary SHell"
> The change on August 26, 2022 should have caused a breaking error for someone 
> using the "Policy-compliant Ordinary SHell."  The prompt for "posh" in 
> "org-babel-shell-set-prompt-commands" is valid PowerShell syntax (AFAIKT) and 
> invalid bash/dash syntax:
>
> function prompt { "org_babel_sh_prompt> " }
>
> It's not clear to me what this would do in the "Policy-compliant Ordinary 
> SHell."  In Bash, functions are defined using a form like:
>
> function fname [()] compound-command [ redirections ]

Simply because I struggled to find what is "posh" at the time I wrote that
code. I only found some obscure page (on the web!) saying the posh might
be PowerShell.
My commit a35d16368 did not intend to introduce anything new.

It turns out that we never supported PowerShell and never announced such
support. So we do not really need to support PowerShell.

> * My stance
> The unfortunate reality is we "support" PowerShell currently.  We have code 
> explicitly to handle PowerShell.  Changing that could, technically, break 
> someone's workflow.

We do not. It was just my mistake trying to figure out what is "posh".
Since posh is POSIX-compliant, generic PS1/PS2 variables should work, and we
do not need a special entry in `org-babel-shell-set-prompt-commands' -
we can remove "posh" record from there.

I'd rather keep the value in `org-babel-shell-names' though. It should
do no harm.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
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