Nixpkgs & Standard Library Reference

Name: nixpkgs
Rating: 87
Author: Hetav21

Overview

Reference for the Nixpkgs standard library (lib) functions and package creation using mkDerivation.

1. Nixpkgs Library (`lib`)

Access via pkgs.lib or just lib if passed in arguments.

Common Functions

Category	Function	Usage / Example
Lists	`forEach`	`forEach [1 2] (x: x*2)` -> `[2 4]`
	`filter`	`filter (x: x>1) [1 2]` -> `[2]`
	`unique`	`unique [1 1 2]` -> `[1 2]`
	`optionals`	`optionals bool [ "a" ]` -> `["a"]` or `[]`
	`foldl'`	`foldl' (acc: x: acc + x) 0 [1 2 3]` -> `6`
Strings	`concatStringsSep`	`concatStringsSep "," ["a" "b"]` -> `"a,b"`
	`hasPrefix`	`hasPrefix "foo" "foobar"` -> `true`
	`removeSuffix`	`removeSuffix ".nix" "file.nix"` -> `"file"`
	`lowerChars`	`stringToCharacters "abc"` (Use `toLower` for case)
Attrs	`mapAttrs`	`mapAttrs (k: v: v*2) { a=1; }` -> `{ a=2; }`
	`recursiveUpdate`	`recursiveUpdate {a.b=1;} {a.c=2;}` -> `{a={b=1;c=2;}}`
	`optionalAttrs`	`optionalAttrs bool { a=1; }` -> `{ a=1; }` or `{}`
	`attrNames`	`attrNames { a=1; }` -> `["a"]`
Debug	`trace`	`trace "Output this" value` -> Prints + returns value
	`traceVal`	`traceVal x` -> Prints x and returns x

2. Package Creation (`mkDerivation`)

Template for packaging software with stdenv.

nix

{ lib, stdenv, fetchFromGitHub, openssl, pkg-config, cmake }:

stdenv.mkDerivation rec {
  pname = "my-package";
  version = "1.0.0";

  src = fetchFromGitHub {
    owner = "user";
    repo = "repo";
    rev = "v${version}";
    hash = "sha256-PLACEHOLDER"; # Use lib.fakeSha256 first to get hash
  };

  # Build-time tools (compilers, linters, setup hooks)
  # run on build machine
  nativeBuildInputs = [ 
    pkg-config 
    cmake 
  ];

  # Runtime dependencies (libraries, linked binaries)
  # run on host machine
  buildInputs = [ 
    openssl 
  ];

  # Common phases (override only if needed)
  # configurePhase = ''./configure --prefix=$out'';
  # buildPhase = ''make'';
  
  # Custom install phase example
  installPhase = ''
    runHook preInstall
    
    mkdir -p $out/bin
    cp bin/my-tool $out/bin/
    
    runHook postInstall
  '';

  meta = with lib; {
    description = "A short description";
    homepage = "https://github.com/user/repo";
    license = licenses.mit;
    maintainers = with maintainers; [ maintainer-name ];
    platforms = platforms.linux;
  };
}

Dependency Types Reference

Attribute	Use For	Examples
`nativeBuildInputs`	Tools needed during build (host platform)	`pkg-config`, `cmake`, `ninja`, `git`
`buildInputs`	Libraries/tools linked at runtime (target platform)	`openssl`, `gtk3`, `glibc`, `python3`
`propagatedBuildInputs`	Dependencies needed by dependents	Python libs, Rust libs

3. Overlays

How to modify or extend nixpkgs.

nix

final: prev: {
  # Add new package
  my-package = final.callPackage ./pkgs/my-package {};

  # Override existing package
  hello = prev.hello.overrideAttrs (old: {
    src = ...;
    patches = (old.patches or []) ++ [ ./fix.patch ];
  });
}