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Basics

Given a hello world example, click on the end of each line to get an explanation:

devenv.nix
{ pkgs, ... }: # (1)!

{ # (2)!
  env.GREET = "hello"; # (3)!

  packages = [ pkgs.jq ];

  enterShell = ''
    echo $GREET
    jq --version
  ''; # (4)!
}
  1. devenv.nix is a function with inputs. pkgs is an input passed as a special argument to the function. We use a special input ... at the end as a catch-all to avoid enumerating all of the inputs.
  2. Our function is returning an attribute set, similar to an object in JSON.
  3. Attributes can be nested and have similar values as in JSON.
  4. Values can refer to the inputs. See Inputs for how to define inputs.

enterShell allows you to execute bash code once the shell activates, while env allows you to set environment variables:

$ devenv shell
Building shell ...
Entering shell ...

hello
jq-1.6

(devenv) $ echo $GREET
hello

See Nix language tutorial for a 1-2 hour deep dive that will allow you to read any Nix file.

Environment Summary

If you'd like to print the summary of the current environment:

$ devenv info
...

# env
- DEVENV_DOTFILE: .../myproject/.devenv
- DEVENV_ROOT: .../myproject
- DEVENV_STATE: .../myproject/.devenv/state
- GREET: hello

# packages
- jq-1.6

# scripts

# processes

CLI Options Overrides

New in 1.6

You can override configuration options temporarily using the --option flag:

$ devenv shell --option env.GREET:string Hello --option languages.rust.enable:bool true

The option requires you to specify the inferred Nix type:

  • :string for string values
  • :int for integer values
  • :float for floating-point values
  • :bool for boolean values (true/false)
  • :path for file paths (interpreted as relative paths)

This is useful for temporarily changing the configuration without modifying your devenv.nix file, such as when testing different configurations or creating option matrices.