1.4 Your first Nix commands: nix run and nix shell

You just installed Nix, now what? This lesson shows the two commands that make Nix useful within minutes: nix run to launch any program from nixpkgs without installing it, and nix shell to open a temporary shell where the tool simply exists. Along the way you learn what nixpkgs#hello actually means, and how to run an older version of a package on purpose.

In this video

• Running a program straight from nixpkgs with nix run: nothing installed, nothing left behind
• What the # in nixpkgs#hello really is, and where the name nixpkgs comes from (hint: there is a registry)
• The small -- detail that decides whether an argument goes to Nix or to the program, a classic beginner trap
• Getting an old package version by pointing at a different nixpkgs branch: ripgrep 13 and 15 on the same machine, no conflict
• Temporary shells with nix shell: what happens to your PATH, how shells nest, a bash trick for several packages at once, and the shorter classic nix-shell -p the instructor uses daily

After this lesson

You can try out any program from nixpkgs on demand, in the version you want, without installing anything or cleaning up afterwards.