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Basic conceptsshare

There are 4 concepts that are fundamental to garn:

There's another basic concept called Project that is used to bundle instances of the above entities and give them structure. Projects are described at the bottom in the Projects section.

All of these concepts are implemented as typescript types. Feel free to browse the API docs as well.


(See also the API docs.)

Environments define what is available to a computation. For example they can contain compilers and developer tools that you want to use on a project, but they may also define other things like environment variables that need to be set.

Running garn enter in a shell will add whatever the Enviroment provides to the shell environment that you're in. That means you can still use your local developer tools, like your editor, etc., but will also have access to everything provided by the Environment you entered.

The garn library provides a special environment called emptyEnvironment. As you might have guessed it's an Environment that doesn't provide anything.

Environments can also be used to create other things that then make use of what the Environments provide. For example Checks, which are our next topic.


(See also the API docs.)

Checks are commands (usually shell commands) that are used to define reproducible, automated tests or other checks. They run in a sandbox, which means they don't have access to your locally installed tools, nor to your local file system. Instead they are always based on an underlying Environment, and through that will have access to exactly the tools that the environment provides. In addition, a copy of your source files is provided in the sandbox. That gives you the ability to define automated Checks on your source files.

You can run Checks with garn check.

Running Checks in a sandbox has its downsides, for example some tests require internet access. The big advantage is that these Checks are almost perfectly reproducible, since the sandbox they run in is very controlled. So a Check that fails or passes on one machine will behave the same on any other machine.

This also means that running these checks on a CI system (for example is very easy and requires no additional configuration.


(See also the API docs.)

Executables are commands (usually shell snippets) that are being run on your local machine (not in a sandbox). They are based on an underlying Environment, and can make use of e.g. the tools that Environments provide. You can use Executables for a variety of purposes:

  • Running your projects main executable during development,
  • Running a code formatter,
  • Running a code generator,
  • Spinning up a database for development,
  • etc.

Here's a small example:

import * as garn from "";

export const hello ="echo Hello, world!");

You can run Executables with garn run.


(See also the API docs.)

Packages are instructions to garn about how to build a set of files. For example for a Go backend a package would define how to compile it into executables. For an Npm project it may define how the project can be bundled into a set of files that can be served by a webserver.

The build scripts of Packages are being run in a sandbox (same as Checks). That means they have access to a copy of your source files, but not to the internet or your local file system. This makes your builds almost perfectly reproducible.

You can build Packages with garn build.


(See also the API docs.)

Projects are used to combine Environments, Checks, Executables and Packages into a single entity. A Project can contain any number of these entities. So for example it can contain multiple Checks, which you can all run at once with garn check <projectName>. It can contain multiple Packages that you can all build with garn build <projectName>.

Projects can have a default Enviroment (aptly called defaultEnvironment), which allows you to call garn enter on a project. Similarly they can also have a default Executable (called defaultExecutable), which allows you to call garn run on a project.

Usually you create Projects through language specific helper functions, for example garn.javascript.mkNpmProject. Here's an example of an Npm Project that contains a few Checks and adds a developer tool to its default environment:

import * as garn from "";
import * as pkgs from "";

export const project = garn.javascript
    src: ".",
    description: "An Npm frontend",
    nodeVersion: "18",
  .addCheck("test", "npm run test")
  .addCheck("tsc", "npm run tsc")
  .addCheck("no todos allowed", "! rg --glob !node_modules -i todo .");

export const dev ="npm install ; npm run dev");

With this garn.ts file:

  • garn enter project will enter a shell with node, npm and ripgrep installed.
  • garn check project will
    • run the tests,
    • typecheck the project (with tsc).
    • search for todos (with ripgrep) and fail if there are any.
  • garn run dev will run the server locally in dev mode.