xdg-utils

xdg-utils provides the official utilities for managing XDG MIME Applications.

xdg-desktop-menu(1) - Install desktop menu items
xdg-desktop-icon(1) - copies desktop entries to the user's desktop
xdg-email(1) - Compose a new email in the user's preferred email client, potentially with subject and other info filled in
xdg-icon-resource(1) - Install icon resources
xdg-mime(1) - Query and install MIME types and associations
xdg-open(1) - Open a file or URI in the user's preferred application
xdg-screensaver(1) - Enable, disable, or suspend the screensaver
xdg-settings(1) - Get or set the default web browser and URL handlers

Installation

Determine a file's MIME type:

$ xdg-mime query filetype photo.jpeg
image/jpeg

Determine the default application for a MIME type:

$ xdg-mime query default image/jpeg
gimp.desktop

Change the default application for a MIME type:

$ xdg-mime default feh.desktop image/jpeg

xdg-open is a resource opener that implements XDG MIME Applications and is used by many programs, see xdg-open(1) for the usage.

xdg-open is desktop-environment-independent in the sense that it attempts to use each environment's native default application tool.

If no desktop environment is detected, MIME type detection falls back to using file which—ironically—does not implement the XDG standard. If you want xdg-open to use XDG MIME Applications without a desktop environment, you will need to install perl-file-mimeinfo or switch to one of the resource openers that support XDG MIME Applications.

Shortcut to open all web MIME types with a single application:

$ xdg-settings set default-web-browser firefox.desktop

Shortcut for setting the default application for a URL scheme:

$ xdg-settings set default-url-scheme-handler irc xchat.desktop