File extension associations with applications.

[halfshavedyaks]

I need to associate different file extensions with different apps for opening the files.

There are many many different types of text files, the contents are all essentially plain text, but they have different purposes and need to be opened in different apps.

It isn't reasonable in this case to expect the OS to correctly analyse the file when it may be something obscure and there are probably hundreds of different types of text files

In any case I want it to take my word for the type of file it is and rely on the extension rather than attempt a file analysis.

Specifically I want to associate the extension .scad with Openscad (which I run from an appimage) but not affect any other plain text files with no extension or different extensions.

If I change a .scad file in properties to open with Openscad as default then ALL plain text files attempt to open with Openscad from then on.

Similarly I want to associate whatever other extensions with specific apps even when the contents are all just plain text.

I have looked in ~/.config/mimeapps.list but I have not had any success editing that manually and I can't find a guide to the syntax.

The whole issue seems very confused between trusting a file extension to identify the file type and analyzing the file. I want it to rely on the extension by preference and only revert to contents analysis if there is no extension ( or maybe if it is is obviously incorrect such as a binary file with a .txt suffix)

I'm using Mint 19 Cinnamon

[Flemur]

The whole issue seems very confused between trusting a file extension to identify the file type and analyzing the file.

"Confused" is exactly right. The mime implementation is a complicated mess.

I want it to rely on the extension by preference and only revert to contents analysis if there is no extension ( or maybe if it is is obviously incorrect such as a binary file with a .txt suffix)

That would be too easy.

I think you need to create a new "mime type", like text/scad; here are some amazingly poorly written instructions:
https://help.ubuntu.com/community/AddingMimeTypes

About half-way down ("Another way to add a MIME Type") it says the instructions up to that point don't work. They didn't work for me, so ignore the top half.

And you're in luck - he's adding the "scad" file type!

Edit: I tried the "Another way" and it didn't work either; the " update-mime-database" command deletes the scad.xml file.

This worked:
In the file

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/usr/share/mime/packages/freedesktop.org.xml

I added

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#NEW 1
  <mime-type type="application/scad">

    <comment>Scad</comment>
    <acronym>Scad</acronym>
    <expanded-acronym>Scad</expanded-acronym>
    <sub-class-of type="text/plain"/>
    <glob pattern="*.scad"/>
  </mime-type>
#NEW 2

after "TriG RDF" type (about line 6438), so it'd be after other "text" values.
Then run

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sudo update-mime-database /usr/share/mime

And now a regular text file aa.scad opens with abiword and aa.txt opens with leafpad by default (just double-click)

Free advice: make a backup copy of freedesktop.org.xml before you edit it!

More free advice:
I made the association with aa.scad by file-browser->rt-click->open with (choose, e.g. abiword) -> set as default , and in

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.config/mimeapps.list

this line is under [Default...] AND under [Added...]

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application/scad=abiword.desktop;

A regular text file opens with leafpad.

[Flemur]

I think the second part of that ubuntu "help" might work - IF YOU PUT THE XML FILE IN
/usr/share/mime/packages
and NOT where they said to:
/usr/share/mime/application,
where it will get silently erased (the files there say "automatically generated, don't edit")

[halfshavedyaks]

wow thanks - your method worked. (I haven't looked at the link to the ubuntu help)

I just added the definition you gave at the end of the freedesktop file so I can find it again.

there's 40k lines in my freedesktop file, much of it much more niche than openscad and with support for loads of languages I will never use.

seems like some optimisation might be in order.

when I updated I got this:

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sudo update-mime-database /usr/share/mime
Unknown media type in type 'all/all'
Unknown media type in type 'all/allfiles'

not sure what that is supposed to mean, but the file association now seems to work and I assume I can use the same process for other file types.