Scripts

Most projects out there have a bunch of shell scripts lying around.

Questions arise as to where to define scripts and how to provide the tooling to make sure they work for all developers.

A simple example defining silly-example script:

devenv.nix

{ pkgs, ... }:

{
  packages = [ pkgs.curl pkgs.jq ]; # (1)!

  scripts.silly-example.exec = ''
    curl "https://httpbin.org/get?$1" | jq '.args'
  '';
}

See Packages for an explanation.

Since scripts are exposed when we enter the environment, we can rely on packages executables being available.

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

(devenv) $ silly-example foo=1
{
  "foo": "1"
}

Aliases & args

Here's an example that shows how to define an alias & forward arguments:

scripts.foo.exec = ''
  npx @foo/cli "$@";
'';

Runtime packages

Sometimes you need packages available only when a specific script runs, without adding them to the global environment. You can specify runtime packages using the packages attribute:

devenv.nix

{ pkgs, ... }:

{
  scripts.analyze-json = {
    exec = ''
      # Both curl and jq are available when this script runs
      curl "https://httpbin.org/get?$1" | jq '.args'
    '';
    packages = [ pkgs.curl pkgs.jq ];
    description = "Fetch and analyze JSON";
  };
}

The packages attribute ensures these tools are available in the script's PATH without polluting the global development environment.

Pinning packages inside scripts

Alternatively, you can directly reference package paths in your script:

devenv.nix

{ pkgs, ... }:

{
  scripts.silly-example.exec = ''
    ${pkgs.curl}/bin/curl "https://httpbin.org/get?$1" | ${pkgs.jq}/bin/jq '.args'
  '';
}

When a package is interpolated in a string, you're referring to the path where it is located.

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

(devenv) $ silly-example foo=1
{
  "foo": "1"
}

Using your favourite language

Scripts can also execute using a package and have a description, which can be useful in your enterShell.

Consider using tasks for shell initialization

For operations that need to run when entering the shell, consider using tasks with the before attribute instead of enterShell. Tasks provide better control over execution order and dependencies.

devenv.nix

{ pkgs, config, lib, ... }:

{
  scripts.python-hello = {
    exec = ''
      print("Hello, world!")
    '';
    package = config.languages.python.package;
    description = "hello world in Python";
  };

  scripts.nushell-greet = {
    exec = ''
      def greet [name] {
        ["hello" $name]
      }
      greet "world"
    '';
    package = pkgs.nushell;
    binary = "nu";
    description = "Greet in Nu Shell";
  };

  enterShell = ''
    echo
    echo 🦾 Helper scripts you can run to make your development richer:
    echo 🦾
    ${pkgs.gnused}/bin/sed -e 's| |••|g' -e 's|=| |' <<EOF | ${pkgs.util-linuxMinimal}/bin/column -t | ${pkgs.gnused}/bin/sed -e 's|^|🦾 |' -e 's|••| |g'
    ${lib.generators.toKeyValue {} (lib.mapAttrs (name: value: value.description) config.scripts)}
    EOF
    echo
  '';
}

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

🦾 Helper scripts you can run to make your development richer:
🦾
🦾 python-hello     Hello world in Python
🦾 nushell-greet    Greet in Nu Shell

(devenv) $