NixOS's reproducibility makes it ideal for building development environments. However, if you're used to other distros, you may encounter problems because NixOS has its own logic. We'll briefly explain this below.
On NixOS, it's recommended to only install common tools in the global environment, such as `git`, `vim`, `emacs`, `tmux`, `zsh`, etc. The development environment of each language should be an independent environment for each project.
You should NOT install the development environment of each language in the global environment. The project environment should be completely isolated from each other and will not affect each other.
The simplest way to create a development environment is to use `nix shell`. `nix shell` will create a shell environment with the specified Nix package installed.
Here's an example:
```shell
# hello is not available
› hello
hello: command not found
# Enter an environment with the 'hello' and `cowsay` package
› nix shell nixpkgs#hello nixpkgs#cowsay
# hello is now available
› hello
Hello, world!
# ponysay is also available
› cowsay "Hello, world!"
_______
<hello>
-------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
```
`nix shell` is very useful when you just want to try out some packages or quickly create a clean environment.
`nix shell` is simple and easy to use, but it's not very flexible, for a more complex development environment, we need to use `pkgs.mkShell` and `nix develop`.
We can create a development environment using `pkgs.mkShell { ... }` and open an interactive Bash shell of this development environment using `nix develop`.
To see how `pkgs.mkShell` works, let's take a look at [its source code](https://github.com/NixOS/nixpkgs/blob/nixos-23.05/pkgs/build-support/mkshell/default.nix).
`pkgs.mkShell { ... }` is a special derivation (Nix package). Its `name`, `buildInputs`, and other parameters are customizable, and `shellHook` is a special parameter that will be executed when `nix develop` enters the environment.
Create an empty folder, save the above configuration as `flake.nix`, and then execute `nix develop` (or more precisely, you can use `nix develop .#default`), the current version of nodejs will be outputed, and now you can use `node``pnpm``yarn` seamlessly.
## Creating a Development Environment with `pkgs.runCommand`
The derivation created by `pkgs.mkShell` cannot be used directly, but must be accessed via `nix develop`.
It is actually possible to create a shell wrapper containing the required packages via `pkgs.stdenv.mkDerivation`, which can then be run directly into the environment by executing the wrapper.
Using `mkDerivation` directly is a bit cumbersome, and Nixpkgs provides some simpler functions to help us create such wrappers, such as `pkgs.runCommand`.
Example:
```nix
{
description = "A Nix-flake-based Node.js development environment";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
};
outputs = { self , nixpkgs ,... }: let
# system should match the system you are running on
Then execute `nix run .#dev` or `nix shell .#dev --command 'dev-shell'`, you will enter a nushell session, where you can use the `node``pnpm` command normally, and the node version is 20.
Add the above configuration to any NixOS Module, then deploy it with `sudo nixos-rebuild switch`, and you can enter the development environment directly with the `dev-shell` command, which is the special feature of `pkgs.runCommand` compared to `pkgs.mkShell`.
Now let's take a look at `nix develop`, first read the help document output by `nix develop --help`:
```
Name
nix develop - run a bash shell that provides the build environment of a derivation
Synopsis
nix develop [option...] installable
# ......
```
It tells us that `nix develop` accepts a parameter `installable`, which means that we can enter the development environment of any installable Nix package through it, not just the environment created by `pkgs.mkShell`.
By default, `nix develop` will try to use the following attributes in the flake outputs:
-`devShells.<system>.default`
-`packages.<system>.default`
If we use `nix develop /path/to/flake#<name>` to specify the flake package address and flake output name, then `nix develop` will try the following attributes in the flake outputs:
-`devShells.<system>.<name>`
-`packages.<system>.<name>`
-`legacyPackages.<system>.<name>`
Now let's try it out. First, test it to confirm that We don't have `c++``g++` and other compilation-related commands in the current environment:
```shell
ryan in 🌐 aquamarine in ~
› c++
c++: command not found
ryan in 🌐 aquamarine in ~
› g++
g++: command not found
```
Then use `nix develop` to enter the build environment of the `hello` package in `nixpkgs`:
```shell
# login to the build environment of the package `hello`
ryan in 🌐 aquamarine in ~
› nix develop nixpkgs#hello
ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
› env | grep CXX
CXX=g++
ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
› c++ --version
g++ (GCC) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
› g++ --version
g++ (GCC) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
```
We can see that the `CXX` environment variable have been set, and the `c++``g++` and other commands can be used normally now.
In addition, we can also call every build phase of the `hello` package normally:
> The default execution order of all build phases of a Nix package is: `$prePhases unpackPhase patchPhase $preConfigurePhases configurePhase $preBuildPhases buildPhase checkPhase $preInstallPhases installPhase fixupPhase installCheckPhase $preDistPhases distPhase $postPhases`
```shell
# unpack source code
ryan in 🌐 aquamarine in /tmp/xxx via ❄️ impure (hello-2.12.1-env)
The `nix build` command is used to build a software package and creates a symbolic link named `result` in the current directory, which points to the build result.
Here's an example:
```bash
# Build the package 'ponysay' from the 'nixpkgs' flake
There are other commands like `nix flake init`, which you can explore in [New Nix Commands][New Nix Commands]. For more detailed information, please refer to the documentation.
- [One too many shell, Clearing up with nix' shells nix shell and nix-shell - Yannik Sander](https://blog.ysndr.de/posts/guides/2021-12-01-nix-shells/)
