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nix

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nix

Nix is a declarative-based distro where in contrary to the standard imperative approach, the whole OS is configured by a file instead of invoking commands first.

There are two ways to use nix:

  • nixOS
  • nix package manager

I prefer to use the nix package manager for now since I do not have the time to invest in learning the OS. Besides, you can install the nix-package manager on any linux distro to try it out.

Nix Package Manager

As a software developer, you are inevitably going to be faced with the problem of managing development environments. X project uses X set of packages, Y project uses Y set of packages, and Z project uses X and Y set of packages.

This becomes a headache and another overhead to the things you are going to think about when developing applications. Thankfully, the nix package manager is here!

One thing I really love about the nix package manager is its declarative nature. No need to check each package.json, requirements.txt, or composer.json files for each project. You can just list them out in a shell.nix or flake.nix file and you’re good to go.

devenv.sh

Imagine this structure for your projects:

/projects
│── main.py
│── project-1/
│   │── shell.nix
│── project-2/
│   │── shell.nix
│── project-3/
│   │── shell.nix
│── project-4/
│   │── shell.nix
│   │── ...
│── ...

Imagine you are frequently switching between projects 1 to 4, and everytime you switch, you would have to activate the shell.nix for each project. That would be a hassle wouldn’t it? That’s where devenv.sh comes in, I used this for a while to test out the power of nix and it was really cool. Here are some pros and cons:

PROS

  • Automatic shell activation
  • Per project dependencies
  • No base shell conflict

CONS

  • Too many files involved in configuration (devenv.nix, devenv.lock, .envrc, .devenv, etc.)
  • Too many dependencies (direnv, devenv, nix, etc.)

In my opinion, the cons aren’t too bad, but the second con made me stop using it since I would have to maintain direnv and devenv separately.

Installation

Here is how to install devenv.sh

Install nix

sh <(curl -L https://nixos.org/nix/install) --daemon
 
# or in arch
 
sudo pacman -S nix

Install devenv

nix-env --install --attr devenv -f https://github.com/NixOS/nixpkgs/tarball/nixpkgs-unstable
 
# or in arch
 
sudo pacman -S devenv

Install direnv

curl -sfL https://direnv.net/install.sh | bash
 
# or in arch
 
sudo pacman -S direnv

Put this in your bashrc, and source it

eval "$(devenv direnvrc)"
use devenv

Usage

In order to create a devenv, you run the command:

devenv init

It’s best to do this in a project root folder. The above command will create multiple files:

  • devenv.nix
  • devenv.yaml
  • .envrc
  • .gitignore

After you have initialized the devenv, you can then edit the devenv.nix file to add packages to the env.

{ pkgs, ... }: 
 
{ 
  env.GREET = "hello"; 
 
  packages = [ pkgs.jq ]; # Add your packages here.
  # You can browse nix packages for packages you want to add.
 
  enterShell = ''
    echo $GREET
    jq --version
  ''; 
}

To start the shell, just invoke the command:

devenv shell

NOTE

If you installed direnv with the steps above, you would notice that there will be logs that would show activating the env upon changing the devenv.nix file.

To check the current devenv details, you can run:

devenv info

If you have direnv installed, you might notice that the shell prints out a lot of logs when activating an environement You can suppress it by adding this to your ~/.config/direnv/direnv.toml fil:

hide_env_diff = true

Extra info

Updating devenv

nix-env --upgrade --attr devenv -f https://github.com/NixOS/nixpkgs/tarball/nixpkgs-unstable

Updating devenv inputs

devenv update

Cleaning up devenv (garbage collection)

devenv gc

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