Re: ob-shell: async support in "shell" vs "bash"

[Matt <matt@excalamus.com>]

 ---- On Mon, 10 Jun 2024 04:33:26 +0200  Suhail Singh  wrote --- 
 > On my system both "shell" and "bash" language blocks use "bash"

 > However, the value of org-babel-header-args:lang differs:
 > 
 >     #+begin_src emacs-lisp :results value replace verbatim
 >       org-babel-header-args:shell
 >     #+end_src
 > 
 >     #+RESULTS:
 >     : ((async (yes no)))
 > 
 >     #+begin_src emacs-lisp :results value replace verbatim
 >       org-babel-header-args:bash
 >     #+end_src
 > 
 >     #+RESULTS:
 >     : nil
 > 
 > Is this a bug, or are async blocks only currently allowed in "shell"
 > language blocks and not "bash" language blocks?

Thank you for your message!

:async should work for all shell types.  Are you finding that it's not?

In practice, anything but a "no" or "none" for :async should work (see "org-babel-comint-use-async").  For example, the following should run the block asynchronously:

#+begin_src bash :session *my-bash* :async banana
echo "hi"
sleep 3
echo "bye"
#+end_src

All shell languages use the "explicit-shell-file-name" to define a comint buffer using the "shell" command.  For "shell" blocks, Babel uses whatever the user has set for "explicit-shell-file-name", most likely "shell-file-name" which defaults to /bin/sh.  Many systems symlink /bin/sh to bash for interactive shells.  I suspect this is what's happening on your system.  You can check this with something like 'ls -la' or 'readlink $(which sh)'.

For all other shell languages, "explicit-shell-file-name" gets set to the block language name, literally, when "org-babel-shell-initialize" is called, such as when ob-shell is first loaded.  That word, such as "bash", will resolve according to, I believe, "exec-path" (which is basically PATH).

Regarding org-babel-header-args, "org-babel-header-args:shell" is explicitly set to '((async . ((yes no)))), it seems, to quiet the linter (https://git.savannah.gnu.org/cgit/emacs/org-mode.git/commit/?id=40d1352b).  For other languages, such as "org-babel-header-args:bash", it's set to nil.  AFAICT, what you see are simply the default values.

I'm curious, what caused you to notice this inconsistency?

--
Matt Trzcinski
Emacs Org contributor (ob-shell)
Learn more about Org mode at https://orgmode.org
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