wiki/structured/tools.nix.org
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The basics of Nix package manager

Nix package manager is a great tool for reproducibility as you can easily set up your environment. Taking it up to the next level with NixOS, your whole installation.

Ecosystem

  • Nix has tools to make setting up environments easier with direnv, lorri, and Niv

You can create a reproducible executable that only requires Nix.

#!/usr/bin/env nix-shell
#! nix-shell --pure -i bash -p curl jq fzf findutils

# A quick command line interface for creating a gitignore with the API from https://gitignore.io.
# This script comes with a simple caching to avoid creating too much requests.

set -eo pipefail

CACHE_FILE="${XDG_CACHE_DIR:-$HOME/.cache}/gitignore-io.langs.json"

# Check if the language list is downloaded for the last hour (3600 seconds).
if [ ! -e $CACHE_FILE ] || test $(expr $(date "+%s") - $(date -r $CACHE_FILE "+%s")) -gt 3600
then
    ping "gitignore.io" --count 4 && curl --silent --location --output $CACHE_FILE "https://gitignore.io/api/list?format=json"
fi

KEYS=$(jq 'keys | .[] | @text' --raw-output $CACHE_FILE | fzf --multi | while read lang; do echo " .[\"$lang\"].contents"; done | paste -s -d ',')

jq "$KEYS" --raw-output $CACHE_FILE

Components of the package manager

Holistically, Nix is made up of at least four components: the store, the language, the derivations, and the sandbox.

  • The store is a immutable centralized location where all of the outputs are placed.
  • The derivations are essentially build instructions.
  • The language (also called as Nix but we'll refer to it as Nixlang) is a domain-specific language for creating derivations.
  • The build process can be locked in a sandbox, improving the reproducibility of a setup and lowering the attack surface for a malicious package.

Overlays

You can override values in Nix as a way to customize nixpkgs. For example, if you want to use a different version from the nixpkgs channel, you can change the appropriate value.

let overlay = self: super:
      {
        ncmpcpp = super.ncmpcpp.override { visualizerSupport = true; };
      }

For another example, you can see some examples from Neovim and Veloren (which also uses Nix flakes).

You can set overlays automatically either by setting nixpkgs.overlays from your system configuration or ~/.config/nixpkgs/overlays/ folder for user-specific settings. You could also set overlays for standalone Nix code similarly through the overlays key — e.g., import <nixpkgs> ? { overlays = (self: super: { } ); };.