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