How to install Fish Shell on Debian 10 Buster

echo 'deb http://download.opensuse.org/repositories/shells:/fish:/release:/3/Debian_10/ /' | sudo tee -a /etc/apt/sources.list
wget -q -O - https://download.opensuse.org/repositories/shells:fish:release:3/Debian_10/Release.key | sudo apt-key add -
sudo apt update
sudo apt install fish

Then to make fish default for root and my user, I do:

chsh --shell $(which fish)
sudo chsh --shell $(which fish)

And I logout and login again.

Notes

The option -O - in wget means that it will directly print content of file rather than save it. And -q (quiet mode) means that it won’t print loading bar for the download.

Because the repository of fish is in HTTP, it is not necessary to install the apt-transport-https package.