If you are using linux machine chances are that you are already using xdg-open.

xdg-open is a utility used by system to open a file or URL in the user’s preferred application.

To run a specific program for a given type of file or URL all you have to do is create a .dekstop file and configure so that xdg-open can run mentioned program for you.

To do that create first a desktop file.

Here is a example of bombadillo.desktop file to execute bombadillo program for any URL starting with gopher/gemini/finger protocol.

[Desktop Entry]
Type=Application
Name=Bombadillo
GenericName=Non-Web Browser
Comment=View gopher, gemini, finger, telnet, http(s) sites over the internet
Terminal=true
Categories=Network;WebBrowser;ConsoleOnly;
Exec=bombadillo -t %u
Icon=bombadillo-icon
MimeType=x-scheme-handler/gopher;x-scheme-handler/gemini;x-scheme-handler/finger;

Note - Terminal=true is needed so that xdg-open can spawn a terminal and execute program in it.

Copy file in .local/share/applications in your home directory.

Run below command to configure this desktop file to gemini URL.

xdg-mime default bombadillo.desktop x-scheme-handler/gemini

This should work whenever next time you try to open any URL starting with “gemini://”.