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Run Tasks

Monorepos can have hundreds or even thousands of projects, so being able to run npm scripts against all (or some) of them is a key feature of a tool like Lerna.

Definitions

  • Command - anything the developer types into the terminal (e.g., lerna run build --scope=header --concurrency=5).
  • Target - the name of an npm script (e.g., build)
  • Task - an invocation of an npm script (e.g., header:build).

Example Repository

Examples are based on this repository, so feel free to clone it and follow along.

Run Everything

Each project has the test and build scripts defined.

Run:

npx lerna run build

This will build the projects in the right order: footer and header and then remixapp.

Terminal Output
    ✔  header:build (501ms)
✔ footer:build (503ms)
✔ remixapp:build (670ms)

—————————————————————————————————————————————————————————————————————————————

> Lerna (powered by Nx) Successfully ran target build for 3 projects (1s)

Note that Lerna doesn't care what each of the build scripts does. The name build is also not special: it's simply the name of the npm script.

Run a Single Task

While developing you rarely run all the builds or all the tests. Instead, you often run things only against the projects you are changing. For instance, you can run the header tests like this:

npx lerna run test --scope=header

Run Tasks Affected by a PR

You can also run a command for all the projects affected in your PR like this:

npx lerna run test --since=origin/main

Learn more here.

Control How Tasks Run

For more control over the order tasks are executed, edit the Task Pipeline Configuration.

To speed up your task execution, learn how to Cache Task Results and Distribute Task Execution

Automatic loading of .env files

By default the modern task runner powered by Nx will automatically load .env files for you. You can set --load-env-files to false if you want to disable this behavior for any reason.

For more details about what .env files will be loaded by default please see: https://nx.dev/recipes/environment-variables/define-environment-variables