2. Run a program with Nix
→ Use the nix run command to run a program from Nixpkgs
→ Learn about Nix flakes and packages
→ Download and run a program from Nixpkgs
In the last section, we installed Nix using the Determinate Nix Installer. Now we can dive in and use Nix to run an actual program. Let’s try running the delightful ponysay:
echo "Hello Nix" | nix run "https://flakehub.com/f/NixOS/nixpkgs/*#ponysay":rocket: Success! You should see a charming equine greeting in your console.
The first time you run a program using nix run it’s likely to be a slow
operation. That’s because Nix needs to build the program’s package
from scratch—or download it from a known cache—and store it in
the Nix store. This is in contrast to most package managers,
which install things more quickly because they download pre-built archives
like tarballs. Future nix run invocations should be instantaneous, as Nix
doesn’t need to build the package again.
Explanation
What happened here? The Nix CLI did a few things:
- It used the
nixpkgsflake reference to pull in some Nix code and targeted theponysayflake output (more on this later). - It built the
ponysaypackage and stored the result in the Nix store. - It ran the executable at
bin/ponysayfrom theponysaypackage.
In Nix, every program is part of a package.
Packages are built using the Nix language.
The ponysay package has a single program (also called ponysay) but packages can contain multiple programs as well as man pages, configuration files, and more.
The ffmpeg package, for example, provides both ffmpeg and ffprobe.
You may have noticed that nix run doesn’t require anything like a nix install command.
This makes it handy for use cases like shell scripting or experimenting with in-progress tools.
For more on nix run, see Using Nix to run software with no installation steps on the Determinate Systems blog.
Congrats! You’ve just run a program using the Nix CLI and learned a little bit about some core Nix concepts. You’re now ready to explore Nix development environments.