Nix cheat sheet

Most used commands

• Install: nix-env -i -f https://github.com/NixOS/nixfmt/archive/master.tar.gz → Install the given package
  • Alternative: nix search nixpkgs nixfmt then nix profile install nixpkgs#nixfmt
• Garbage collection: nix-store --gc or nix-collect-garbage -d

Nix package management

Most Important Documentation Links

• Nix Docs (Tool, Language): https://nixos.org/manual/nix
• Nixpkgs Docs (Packaging, programs, libraries): https://nixos.org/manual/nixpkgs
• NixOS Docs: https://nixos.org/manual/nixos
• Nixpkgs package and NixOS module search engine: https://search.nixos.org

Imperative Package Management

• Update package list: apt update (happens automatically in Nix)
• Search: apt search <pkgname> | nix search nixpkgs <pkgname>
• Install: apt install <pkgname> | nix profile install nixpkgs#<pkgname>
• Upgrade installed: apt upgrade | nix profile upgrade '*'
• List installed: dpkg -l | nix profile list
• Remove: apt remove <pkgname> | nix profile remove <list-number>
• Rollback: nix profile rollback

Per-Project Shells

• Ad-hoc shell with packages: nix shell nixpkgs#pkg1 or nix shell nixpkgs#{pkg1,pkg2}
• Project-shell with flake: nix develop
• Project-shell with shell.nix or default.nix file: nix-shell

Building Packages

• Build default.nix or default pkg from flake: nix build
• Build specific attributes (flakes): nix build .#pkg1 .#pkg2

Input Management

Flakes

• Init flake project: nix flake init
• Init flake-parts project: nix flake init -t github:hercules-ci/flake-parts
• Update flake inputs: nix flake update
• Update and commit lock file: nix flake update --commit-lock-file
• Update specific input: nix flake lock --update-input <name>

Flake References

• Flake in current Directory: .
• Local path: [path]:/path/to/repo
• HTTPS URL to flake tarball: https://host/flake.tar.gz
• Git Repo via HTTPS: git+https://host/repo
• Git Repo via SSH: git+ssh://git@host/repo
• GitHub Repo: github:owner/repo
• Specific Branch/Tag: github:owner/repo?ref=abc123

Garbage Collection

• Collect unreferenced and store paths: nix-collect-garbage
• Also collect old profile/system generations: nix-collect-garbage -d
• Only delete up to 50GB: nix-collect-garbage --max-freed 50G
• Find and link identical files: nix-store --optimise
• Print all GC roots: nix-store --gc --print-roots

Nix REPL

• Start Nix REPL: nix repl
• Load local Flake: :lf
• Build derivation: :b attribute.with.derivation
• Build & install derivation: :i attribute.with.derivation
• Fully print expression: :p some.expression
• Show documentation on built-in function: :doc builtins.listToAttrs
• Show REPL help: :?

Nix language

Most Important Documentation Links

• Nix builtins functions: https://nixos.org/manual/nix/stable/language/builtins
• Nixpkgs function library: https://nixos.org/manual/nixpkgs
• Nixpkgs function search engine: https://noogle.dev

Types

• String: "this is a string"
• Multi-line String (double single-quotes):
  nix ''foo bar''
• Boolean: true, false
• Null: null
• Integer: 123, -123
• Float: 3.14
• Path: /an/absolute/path, ./relative/path, ../dir/up/and/down
• Simple attribute set: { a = 1; b = 2; }
• Nested attribute set: { a = 1; b = { c = 3; d = 4; }; }
• Recursive attribute set: rec { x = 1; y = x + 1; }
• List: [ 3 2.0 "one" null ]

Syntax

• Comment: # a single-line comment or /* a multi-line comment */
• If-then-else: if x > 3 then 10 else -10
• Local variables:
  nix let x = 1; y = 2; in x + y # ➡ returns 3
• Attribute set assignment:
  nix { x = 1; y = 2; } # ➡ returns { x = 1; y = 2; }
• Update operator: { x = 1; y = 2; } // { x = 2; }
• Result: { x = 2; y = 2; }
• Attribute set has-operator:
  nix let set = { x = 1; }; in set ? x # ➡ returns true

Reference Attribute Keys

• Reference attribute keys:
  nix s = { x = { y = 1; }; }; s.x.y # ➡ returns 1
• Reference optional attribute keys:
  nix let set = { x = 1; }; in set.y or 2 # ➡ returns 2

List Concatenation

• Concatenate lists: [ 1 2 ] ++ [ 3 4 ] # ➡ returns [ 1 2 3 4 ]

Inheritance

• Inherit:
  nix let x = 1; in { inherit x; } # same as let x = 1; in { x = x; }
• Inherit from scope:
  nix let x = { y = 1; }; in { inherit (x) y; } # same as let x = { y = 1; }; in { y = x.y; }

Functions

• Simple function in Python style:
  nix let f = x: x + 1; in f 1 # ➡ returns 2
• Function with 2 parameters (Python style):
  nix let f = x: y: x + y; in f 1 2 # ➡ returns 3
• Function with named parameters:
  nix let f = { x, y }: x + y; in f { x = 1; y = 2; } # ➡ returns 3
• Match specific parameters and ignore others:
  nix let f = { x, ... }: x; in f { x = 1; y = 2; z = 10; } # ➡ returns 1
• Function with default values:
  nix let f = { x, y ? 2 }: x + y; in f { x = 1; } # ➡ returns 3

Other Special Syntax

• String interpolation:
  nix let x = "bar"; in "foo ${x} baz" # ➡ returns "foo bar baz"
• Masking ${...} in a string:
  nix "this is ${masked}" # ➡ returns "this is ${masked}"
• Masking ${...} in double single-quote strings:
  nix ''this is ''${masked}'' ''
• Paths (copied to nix store when referenced):
  /an/absolute/path ./a/relative/path ../dir/up/and/down
• Key from variable in attribute set:
  nix let x = "key"; in { ${x} = "value"; }

Special Built-in Functions

• Import file and return expression:
  nix import ./some/file.nix
• Assertion:
  nix assert 1 + 1 == 2; 10 # ➡ returns 10 without error
• Abort evaluation with error:
  nix abort "this describes the error"
• Throw an exception when referenced:
  nix throw "this describes the exception"

Page last modified: 2025-03-11 18:15:19