Nix

エンジニアのためのWebチートシート

マルチユーザーインストール（推奨）

# Linux / macOS (multi-user, recommended)
sh <(curl -L https://nixos.org/nix/install) --daemon

シングルユーザーインストール

# Single-user (no daemon)
sh <(curl -L https://nixos.org/nix/install) --no-daemon

アンインストール

# macOS
/nix/nix-installer uninstall

~/.config/nix/nix.conf または /etc/nix/nix.conf に設定を記述します。

# ~/.config/nix/nix.conf
experimental-features = nix-command flakes

# Optional settings
max-jobs = auto
sandbox = true
trusted-users = root @wheel
substituters = https://cache.nixos.org
auto-optimise-store = true
keep-outputs = true
keep-derivations = true

Flakeの基本的なファイル構造です。

{
  description = "My project flake";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in {
        packages.default = pkgs.hello;

        devShells.default = pkgs.mkShell {
          buildInputs = [ pkgs.nodejs pkgs.yarn ];
        };

        apps.default = {
          type = "app";
          program = "${pkgs.hello}/bin/hello";
        };
      }
    );
}

Flakeの依存関係（inputs）の記述パターンです。

inputs = {
  # GitHub repository (default branch)
  nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";

  # GitHub repository (specific branch)
  nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixos-unstable";

  # Follow another input's nixpkgs
  home-manager = {
    url = "github:nix-community/home-manager";
    inputs.nixpkgs.follows = "nixpkgs";
  };

  # Git repository
  my-repo.url = "git+https://example.com/repo.git";

  # Local path
  my-local.url = "path:./subdir";
};

Nix言語の基本的な型とリテラルの書き方です。

# String
"hello world"
''
  multi-line
  string
''

# Integer & Float
42
3.14

# Boolean
true
false

# Null
null

# Path (not a string!)
/etc/nixos/configuration.nix
./flake.nix
~/.config/nix

# List (space-separated, no commas)
[ 1 2 3 "hello" true ]

# Attribute Set (key-value pairs)
{ name = "nix"; version = "2.24"; }

# Nested attribute set
{ a.b.c = 1; }
# equivalent to: { a = { b = { c = 1; }; }; }

# Attribute access
let x = { a = 1; b = 2; }; in x.a  # => 1

# Has attribute operator
{ a = 1; } ? a   # => true

# Merge attribute sets
{ a = 1; } // { b = 2; }  # => { a = 1; b = 2; }

# String interpolation
let name = "world"; in "hello ${name}"

Nix言語の関数（ラムダ式）の定義パターンです。

# Single argument
x: x + 1

# Multiple arguments (curried)
x: y: x + y

# Apply function
let add = x: y: x + y; in add 1 2  # => 3

# Attribute set argument (destructuring)
{ name, age }: "I am ${name}"

# With default values
{ name, age ? 25 }: "Age: ${toString age}"

# With extra attributes allowed
{ name, ... }: name

# Named attribute set argument
args@{ name, age }: args

# Equivalent
{ name, age } @ args: args

# builtins (commonly used)
builtins.map (x: x * 2) [ 1 2 3 ]  # => [ 2 4 6 ]
builtins.filter (x: x > 2) [ 1 2 3 4 ]  # => [ 3 4 ]
builtins.length [ 1 2 3 ]  # => 3
builtins.attrNames { a = 1; b = 2; }  # => [ "a" "b" ]
builtins.hasAttr "a" { a = 1; }  # => true
builtins.toString 42  # => "42"
builtins.toJSON { a = 1; }  # => "{\"a\":1}"
builtins.readFile ./file.txt
builtins.fetchurl "https://example.com"

従来のshell.nixを使った開発環境の定義です。

# shell.nix
{ pkgs ? import <nixpkgs> {} }:

pkgs.mkShell {
  buildInputs = with pkgs; [
    nodejs_22
    yarn
    python3
    postgresql
  ];

  shellHook = ''
    echo "Dev environment loaded!"
    export DATABASE_URL="postgresql://localhost/mydb"
  '';
}

Flakeを使った開発環境の定義です。

# flake.nix
{
  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs = { nixpkgs, flake-utils, ... }:
    flake-utils.lib.eachDefaultSystem (system:
      let pkgs = nixpkgs.legacyPackages.${system};
      in {
        devShells.default = pkgs.mkShell {
          buildInputs = with pkgs; [
            nodejs_22
            yarn
            python3
          ];
          shellHook = ''
            echo "Dev environment loaded!"
          '';
        };
      }
    );
}

direnvを使ってディレクトリに入ると自動で環境をロードします。

# Install direnv & nix-direnv
nix profile install nixpkgs#direnv nixpkgs#nix-direnv

# .envrc (for Flakes)
use flake

# .envrc (for shell.nix)
use nix

# Allow direnv for the directory
direnv allow

Nixの全パッケージは/nix/store配下にハッシュ付きパスで格納されます。

/nix/store/<hash>-<name>-<version>

# Example
/nix/store/w2dlk3n5p6ak...-nodejs-22.12.0
/nix/store/a9z4q3m8j2bx...-hello-2.12.1

# Key characteristics:
# - Immutable (read-only)
# - Content-addressed (hash of all inputs)
# - Shared across users
# - Dependencies are explicit