[off-topic] remove app association from file extension

[Mihai Moldovan]

* On 4/19/19 11:25 PM, Helmut K. C. Tessarek wrote:
> I want to dissociate the file extension .md from any application.
> After installing Xcode, the .md extension is associated with Xcode.
> Yes, I can change the association to a different application, but I
> don't want an association at all.
> I want macOS to let me choose the app every time I double click on an
> .md file.
> 
> Therefore I have this simple question:
> 
> How do I dissociate a file extension from an application?

Guess what? You can. Once. Not easily, though.

You COULD delete or modify ~/Library/Preferences/com.apple.LaunchServices.plist,
but that would only help for associations you made/changed yourself.

The issue that Xcode's Info.plist file includes MIME type, URI and file
extension specifications that are being registered with... whatever it is,
LaunchServices probably. There's no way of turning off auto-discovery of such
metadata, it seems. To truly get rid of these associations, you'll have to edit
Xcode's Info.plist file and remove them manually. Xcode brings a plist editor,
so the binary format isn't a huge issue - however, the first hurdle would be
file permissions. You'd probably be better off copying its Info.plist file to
your home directory and edit it there. When done, move it back, but make sure
that the file permissions exactly match the original state. I'd say that you
need to remove the CFBundleTypeExtensions entry for "md".

Afterwards, regenerate the database via
/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister
-kill -r -domain local -domain system -domain user and give Finder a nudge using
killall Finder.


Note that this won't solve your general problem. It may unlink Xcode from the
file extension (at least until you update the Xcode installation, which will
bring the automatic association back of course), but once you open it with some
other application, this new preference will be automatically saved in the file I
mentioned at the beginning. Of course there is no way to prevent that from
happening.


Like Ryan said, there's no built-in way to achieve what you want to do. There
are applications like Choosy or Finicky (latter has source code available), but
they only handle URLs. It might be possible to extend the latter one to work on
MIME types/file extensions as well, but is it worth the effort?



Mihai

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