Ubuntu – How to change all file associations (MIME-types) of one particular application in KDE

MIME types are just a way to name types. They don't have anything to do with how the type of a file is determined.

There are two ways to determine the type of a file: a) Look at its extension and hope that it is accurate or b) look at its contents and then guess based on that. If a file has no extension b is the only option.

Many (binary) file formats have a specific header that you can look at to determine their type. This makes option b quite reliable for those types.

Plain text file formats can often be determined by their structure (if a file contains a lot of html tags, it's probably a html file).

On unix and linux systems you can use the file command line utility to find out the type of a file based on its contents.

File manager often use some combination of option a and b (e.g. look at the file extension first, if it's not known (or the file does not have an extension), look at the contents).

A file's type is not stored as metadata on common linux file systems.

Years later, I've made a small utility that scans MIME database (both system and user) and register all known native mime-types in Windows registry.

It uses xdg-open to open a file if there is a default (native) application for that mime type, otherwise uses packagekit to search for a package that can handle that file (just like what Nautilus does). So my initial requirement of registering only extensions that have an installed, native application was not needed anymore. However, an early version of the script did filter only such types. The snippet that made it possible was:

perl -e '
    use strict; use warnings;
    use File::MimeInfo::Magic; use File::MimeInfo::Applications;
    while (my $line = <STDIN>) {
      chomp($line);
      my ($ext, $mime) = (split/\t/, $line);
      my ($def, @apps) = mime_applications_all($mime);
      print "$line\n" if ($def || @apps)
    }'

By default my script only registers native types that have no handler in windows registry, but it can also override such associations (so, for example, jpeg files are opened in native viewer instead of the default Gecko wine browser). It can also ignore some extensions even if they have no handler in windows.

It tries its best to be winemenubuilder-friendly, meaning all associations it creates is not published as native associations (or as x-wine-extension mimetypes) by winemenubuilder, which would be ugly and potentially cause loops. This is very tricky and not yet perfect, specially with mixed-case extensions (.C and .c for example)

That said, I hope this script is helful for everyone:

https://github.com/MestreLion/wine-tools/blob/master/wine-import-extensions

Improvements welcome!