nix3-develop

Start a shell with all dependencies of a package from nixpkgs available

$ nix develop [nixpkgs#pkg]

$ nix develop

$ configurePhase; buildPhase

nix3 develop [options...] [flake-ref]#[devShell-attr]

-c, --command cmd
    Execute cmd in the dev shell instead of interactive shell

--expr
    Treat flake input as Nix expression, not file

--flake url
    Select flake from specified URL

--impure
    Allow access to host environment (unpure)

--ignore-environment
    Clear existing env vars before sourcing shell

-i
    Alias for --impure

--keep-going
    Continue on build errors

--no-use-remote
    Build locally, skip remote cache

--no-write-lock-file
    Skip updating flake.lock

--override-input input flake-ref
    Override input with another flake

--profile path
    Use custom profile for GC root

The nix3 develop (or nix develop in Nix 3.x) command launches an interactive shell with a build environment defined by a Nix flake's devShell output. Flakes provide reproducible, declarative project configurations, specifying inputs (dependencies) and outputs like development shells.

Upon invocation, Nix evaluates the flake, builds the shell derivation (if needed), and sources its setup hook into the current shell. This configures PATH, environment variables, and other necessities for development tasks, such as compiling code or running tests. The environment is isolated yet allows overriding for flexibility.

Key benefits include reproducibility across systems, easy dependency management without global installs, and integration with tools like direnv via shell hooks. It's ideal for Rust, Haskell, or any language supported by Nix packages. Impure mode permits using the host environment alongside the flake shell.

Exiting the shell returns to the parent environment, leaving no persistent changes.

Experimental in Nix <3.0; requires flakes enabled. Multi-flake support limited; impure mode reduces reproducibility. Large shells may build slowly without cache.

nix3 develop .#shell
nix3 develop github:NixOS/nixpkgs/nixos-unstable#gnumake
nix3 develop --impure -c cargo test

Define in flake.nix: outputs = { self, nixpkgs }: { devShell.x86_64-linux = ...; };

Introduced experimentally in Nix 2.4 (2021) with flakes feature flag. Stabilized in Nix 3.0 (2023) as core CLI replacing nix-shell --pure. Evolved for better DX in monorepos and teams.

nix(1), nix-shell(1), nix-build(1), flakes(7)