How to Write a Simple, Cross-Platform Nix Derivation (with Flake Example)

Nix makes packaging software reproducible and portable. Here’s how to create a minimal derivation for a C program, and how to modernize it with flakes for automatic platform detection.

Write Your Program Suppose you have a simple C file, simple.c:

#include <stdio.h>
int main() {
    puts("🐧 Hello! allo, allo!");
    return 0;
}

Write a Build Script Create simple_builder.sh:

export PATH="$coreutils/bin:$gcc/bin"
mkdir -p $out/bin
gcc -o $out/bin/simple $src

Write a Platform-Aware Derivation Create simple.nix that takes system as an argument:

{ pkgs ? import <nixpkgs> { }, system ? builtins.currentSystem }:

pkgs.stdenv.mkDerivation {
name = "simple";
src = ./simple.c;
builder = "${pkgs.bash}/bin/bash";
args = [ ./simple_builder.sh ];
inherit (pkgs) gcc coreutils;
system = system;
}

Build with:

nix-build simple.nix
./result/bin/simple

Or override the platform:

nix-build simple.nix --argstr system x86_64-linux

Use Flakes for Maximum Portability
Tip: Flakes require your project to be in a git repo.

Create flake.nix:

{
description = "Simple C program";
inputs.nixpkgs.url = "github:NixOS/nixpkgs";
outputs = { self, nixpkgs }: {
    packages = nixpkgs.lib.genAttrs [ "x86_64-linux" "aarch64-linux" ] (system:
    let pkgs = nixpkgs.legacyPackages.${system}; in
    pkgs.stdenv.mkDerivation {
        name = "simple";
        src = ./simple.c;
        builder = "${pkgs.bash}/bin/bash";
        args = [ ./simple_builder.sh ];
        inherit (pkgs) gcc coreutils;
        system = system;
    }
    );
};
}

Initialize git and build:

git init  # if not already a git repo
nix build .#simple
./result/bin/simple

Summary
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Use system to make your derivation portable.
With flakes, your build will work on any supported platform—just keep your project in a git repo.
Nix ensures your builds are reproducible and cross-platform, with minimal boilerplate.

Summary#

Summary
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