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5. Search for Nix packages

Quick start / Search for Nix packages
Guide 5 of 8
In this guide

→ Use the nix search command to find packages in Nixpkgs

→ Explore the search.nixos.org web interface

→ Use the nix flake show command to explore packages output by flakes

One great thing about Nix is that there are tons of packages available in the Nix ecosystem that you can use in Nix development environments, in your NixOS installations, and more. While Nixpkgs is by far the largest Nix package collection—over 100,000 packages and counting :sunglasses:—any Nix flake can provide package outputs.

But navigating all of this plenty can be tricky, so in this guide we’ll learn how to search for packages in Nixpkgs using the nix search command and using the web application at search.nixos.org. Then we’ll learn how to explore packages in other flakes.

The nix search command

The Nix CLI has a search command that you can use to search the packages in a flake based on a search term. Let’s start by searching Nixpkgs, which is where we’re mostly likely to find packages we want. This command will tell us if cargo is available in Nixpkgs:

Terminal window
nix search "https://flakehub.com/f/NixOS/nixpkgs/*" cargo

In this command, the nixpkgs flake reference is shorthand for github:NixOS/nixpkgs.

This could take a while

The first time you run nix search, the Nix CLI needs to download the full Nix code contents of Nixpkgs—or whichever flake you’re searching—and then cache it. Future nix search runs for Nixpkgs should be much speedier. Furthermore, Nixpkgs is the largest flake in existence and running nix search on other flakes should be much faster in general.

This brings up many results of the form legacyPackages.{system}.{package}, the first of which should look like this on an Apple Silicon (aarch64-darwin) system:

Terminal window
* legacyPackages.aarch64-darwin.cargo (1.65.0)
  Downloads your Rust project's dependencies and builds your project

The system attribute varies on other platforms (you may see x86_64-linux or something else). After that first result, you should see many others, including packages like cargo-about and cargo-audit.

legacyPackages isn't legacy software

The legacyPackages attribute that you see in the search output is a bit misleading. The packages prefaced with that aren’t “legacy” packages; instead, Nixpkgs uses a special legacyPackages attribute to output packages instead of the usual packages output for reasons laid out here.

You can also output search results as JSON using the --json flag:

Terminal window
nix search nixpkgs cargo --json

This can be useful if you want to parse the output using a tool like jq.

search.nixos.org

The web interface at search.nixos.org has a few advantages over the nix search command:

  • It enables you to select a release channel for Nixpkgs, such as 22.11 and unstable
  • It enables you to search across a range of public flakes beyond Nixpkgs (those flakes are listed here)

Exploring a flake with the nix flake show command

As an example, let’s explore a popular flake for the Wayland window system protocol.

Terminal window
nix flake show "github:nix-community/nixpkgs-wayland"
This could take a while

The first time you run nix flake show, the Nix CLI needs to download the full contents of nixpkgs-wayland—or whichever flake you’re running nix flake show on—and then cache it. Future nix flake show runs for the same flake reference should be much speedier.

When to use nix search vs. nix flake show

Should you use nix flake show or nix search? A good rule of thumb is to always use nix search with Nixpkgs and to initially use nix flake show with other flakes. If the package outputs for nix flake show are big enough to be tricky to navigate, use nix search for that flake instead.

System specificity

One thing you’ll notice about the search output for nix search, search.nixos.org, and nix flake show is that all the packages listed in the query results are for your current system (x86_64-linux for an AMD/Intel Linux system, aarch64-darwin for an Apple Silicon system, and so on). That’s because Nix works in a fundamentally system-specific way. The cargo package on a Linux machine is considered a different package from cargo on a non-Linux system.