nix-shell

• Chroot into a virtual environment with the packages your wish
• Next shells can be nested adding more packages
• References the package files directly from nix-store

nix-shell

{ pkgs ? import <nixpkgs> {} }:

pkgs.mkShell { # mkShell is a helper function
  name="dev-environment";

  # list of pakcages to be installed in the virtual shell
  buildInputs = [
    pkgs.nodejs
  ];
  # Command to run when entering the environment
  shellHook = ''
    echo "Starting the development environment"
  '';
}

packages

# single package
nix-shell --packages "nodejs"
nix-shell -p "nodejs"

# multiple packages
nix-shell -p cowsay lolcat

path

• Determine what to use as source for the packages
• Pick the revision identifier at https://status.nixos.org/
• Pick either the latest release (e.g., nixos-24.05) or the unstable release (nixos-unstable)

# Uses a specific git revision of nixpkgs
nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/2a601aafdc5605a5133a2ca506a34a3a73377247.tar.gz

# Pin to nixpkgs version
nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/tarball/nixos-24.05

run

• Runs a command in the shell environment and exit

nix-shell -p cowsay lolcat --run "cowsay Hey! | lolcat"

pure

• Discard system environment variables
• This way, only the provided packages are available inside of the shell

nix-shell -p git --pure

Nix Shell Scripts

• Assure a reproducible script run
• Leverages shebang
• The -i flag indicates the interpreter for the rest of file

#!/usr/bin/env nix-shell
#! nix-shell -i bash --pure
#! nix-shell -p bash cacert curl jq python3Packages.xmljson
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/2a601aafdc5605a5133a2ca506a34a3a73377247.tar.gz

curl https://github.com/NixOS/nixpkgs/releases.atom | xml2json | jq .

Declarative Shell Environment

• Define the environment declaratively as shell.nix file

{ pkgs ? import <nixpkgs> { } }:

pkgs.mkShellNoCC {
  packages = with pkgs; [
    cowsay
    lolcat
  ];
}

# implies "default.nix" or "shell.nix"
nix-shell

# explicit shell config
nix-shell "my-shell.nix"