Installation

https://nixos.org/download/#nix-install-linux

Creating a shell environment

Let’s run our first programs with Nix. We will be using nix-shell for this.

nix-shell -p cowsay lolcat

Now that we’re inside the shell, we can use them

cowsay Hello, Nix! | lolcat

 _____________
< Hello, Nix! >
 -------------
        \\   ^__^
         \\  (oo)\\_______
            (__)\\       )\\/\\
                ||----w |
                ||     ||

We can simply pipe our echo to lolcat

To run a program once, we can

nix-shell -p hello --run hello

Hello, world!

Ensuring isolation

Sometimes it is necessary to ensure that the nix shell does not contain any packages we have in our own environment. We can pass a --pure flag to ensure only dependencies in shell.nix is considered.

nix-shell --pure

<aside> 💡

• -pure If this flag is specified, the environment is almost entirely cleared before the interactive shell is started, so you get an environment that more closely corresponds to the “real” Nix build. A few variables, in particular HOME, USER and DISPLAY, are retained. Note that ~/.bashrc and (depending on your Bash installation) /etc/bashrc are still sourced, so any variables set there will affect the interactive shell. </aside>

Reproducibility

We would like to have a fully reproducible example would give exactly the same results no matter when or where you run the command. The environment provided would be identical each time.