I guess maybe I should have given a little better description of what I 
tried that did NOT work?  But it's a little off-topic for this mailing 
list.  Nevertheless, here it is...

I created a ~/.mailcap file and put this in it, which I cut and pasted 
from /etc/mailcap:

    application/x-shellscript; emacs27 %s; test=test -n "$DISPLAY"

But obviously that's not going to change anything, since it's already in 
the system mailcap file, /etc/mailcap.  DOH!  And sure enough, running 
'>$ run-mailcap myscript' invokes 'less'.  But what I wasn't expecting 
is that running '>$ update-mime -- local' gives me: "Error: 
'/home/user/.mailcap' is not in required format -- not updated".   Not 
sure why I'm getting that when I cut-and-pasted from /etc/mailcap.

No worries.  I'll look in more depth later.


On 5/23/22 8:40 AM, Craig STCR wrote:
> Thanks all for your help!
>
> On 5/20/22 9:44 PM, Ihor Radchenko wrote:
>> Dear Craig, ... or provide plain/text handler in ~/.mailcap.
>>
> OK, I did a first-try on this and was unsuccessful, but I'm sure it's 
> user error.  I need to refresh my knowledge on how to customize 
> user-local mime database, and that will write-out a new ~/.mailcap, 
> etc, I think?  I've done it before, but it was awhile ago, and I 
> wasn't paying attention to ~/.mailcap when I did it.  I know for Gnome 
> I can create a .desktop file.  But I know there's a way to customize 
> user-local mime database without Gnome desktop. I'll take a closer 
> look when I have a little more time.
>
>
> On 5/20/22 9:44 PM, Ihor Radchenko wrote:
>> However, I am not sure what to do on Windows/Mac.
> Maybe try a quick-and-dirty, cross-platform solution that checks 
> non-binary files for a first-line shebang?  Could use existing Emacs 
> hooks that determine major-mode when opening files.
>
> Again, thanks all for your help!
>
> Best,
> -Craig
>