Nix-build in under 100 lines
The article presents a minimal implementation of the Nix build system core in under 100 lines of code. It distills the fundamental concepts of Nix—derivations, store paths, and build execution—into a compact, educational example. The goal is to demystify Nix's internals by showing how a functional package build can be expressed concisely.
Background
Nix is a purely functional package manager and build system that has gained popularity in the DevOps and software engineering world for its reproducibility guarantees — if a build works on one machine, it should work identically on another. This blog post explores how the core logic of `nix-build` (the tool that actually builds Nix packages) can be reimplemented in under 100 lines of code, demystifying a system many find opaque. The author is a known Nix contributor who frequently writes about the internals of the ecosystem. For context: Nix's build model differs from traditional tools like Make or Docker in that builds run in isolated sandboxes with explicitly declared dependencies (no hidden state), which is what enables reproducibility. The post strips away the complexity of the full Nix codebase to show the fundamental algorithm at work.