xdg-override

Override xdg-open behavior. Because the way it already works is not confusing enough.

How do you change browser in Slack anyway?

What is xdg-open and what xdg-override does?

xdg-open is a GNU/Linux application that "opens" files and URLs in user's preferred application:

For example, open avatar.png in the default image viewer

~ ❯ xdg-open avatar.png

Or open https://freedesktop.org URL in the default browser

~ ❯ xdg-open "https://freedesktop.org"

Most application on GNU/Linux by convention delegate to xdg-open when they need to open a file or a URL. This ensures consistent behavior between applications and desktop environments: URLs are always opened in our preferred browser, images are always opened in the same preferred viewer.

However, there are situations when this consistent behavior is not desired: for example, if we need to override default browser just for one application and only temporarily. This is where xdg-override helps: it replaces xdg-open with itself to alter the behavior without changing system settings.

For example, if our default browser is Firefox, and we want Chromium to be our default browser in Slack messenger, we can launch Slack like this:

~ ❯ xdg-override --match "^https?://" chromium slack

How does it work?

Two words: PATH manipulation.

You can read the explanation of how xdg-override works and about my motivation in my blog post How do you change browser in Slack anyway?

Installation and running

If you use Nix, you can install xdg-override from the flake, or you can try it without installation like this

~ ❯ nix run github:koiuo/xdg-override -- --match "^https://" chromium slack

For everyone else, place the script anywhere you wish and execute it from there. It does not require any configs, and it only creates some temporary files under /tmp.

Usage

~ ❯ xdg-override --help
xdg-override [options...] <app>
  -h, --help
      Show command synopsis.
  -m <regex> <command>, --match <regex> <command>
      Override handling of specific mimetype

Examples

  xdg-override -m "^https?://.*\.youtube.com/" mpv \
               -m "^https?://" firefox \
               thunderbird

Launches thunderbird and
- forces all *.youtube.com URLs to open in mpv
- forces all other URLs to open in firefox

On top of the script, the flake offers a few library functions to be used in NixOS or home-manager config

proxyPkg generates a package which can be installed to the profile to globally override xdg-open behavior:

customXdgOpen = xdg-override.lib.proxyPkg { 
  inherit pkgs; 
  nameMatch = [
    { case = "^https?://.*\.youtube.com/"; command = "mpv"; }
    { case = "^https?://open.spotify.com/"; command = "spotify-open"; }
  ];
};

home.packages = [
    ...
    customXdgOpen
    ...
]

wrapPackage wraps a single package and alters xdg-open behavior just for that single application:

customSlack = (xdg-override.lib.wrapPackage { 
  nameMatch = [
    { case = "^https?://open.spotify.com/"; command = "spotify-open"; }
    { case = "^https?://"; command = "firefox"; }
  ];
} pkgs.slack);

home.packages = [
    ...
    customSlack
    ...
]

Further development

The script is more than sufficient for my needs and I don't plan to add new features to it. Nix library might see some improvements, and as an excercise I might do some polishing and automated testing.

That said, don't hesitate to open an issue if you miss something or have a cool idea.