Parametrize shell escape command

[googly.negotiator862 at aceecat.org]

Dear list,

for my next mutt tweak, my goal is to set up a macro key binding which
will go in the pager keymap and, as its main job, will execute a
<shell-escape>. The part which -- as far as I can see -- is
nontrivial: I need to pass the name of the current folder as an
argument to the executed script.

It is easy enough to set up a series of folder-hook mutt config
commands so that the name ends up in a user mutt variable, say
$my_folder_name. The seeming difficulty is in exporting this value to
the external environment (in the precise Unix sense of this term). So
far, any way I've thought of doing this turned out to only "beg the
question".

If it matters, I only use mutt locally and only on Maildir folders, so
a folder name is always just the name of a subdirectory inside the
directory named by $folder.

-- 
Ian