.env File
Nuxt CLI has built-in dotenv support in development mode and when running nuxi build and nuxi generate.
In addition to any process environment variables, if you have a .env file in your project root directory, it will be automatically loaded at build, dev, and generate time, and any environment variables set there will be accessible within your nuxt.config file and modules.
If you want to use a different file - for example, to use .env.local or .env.production - you can do so by passing the --dotenv flag when using nuxi. For example:
npx nuxi dev --dotenv .env.localJust as above, this will only apply in development mode and when running nuxi build and nuxi generate.
When updating .env in development mode, the Nuxt instance is automatically restarted to apply new values to the process.env.
Note that removing a variable from .env or removing the .env file entirely will not unset values that have already been set.
However, after your server is built, you are responsible for setting environment variables when you run the server. Your .env file will not be read at this point. How you do this is different for every environment. On a Linux server, you could pass the environment variables as arguments using the terminal DATABASE_HOST=mydatabaseconnectionstring node .output/server/index.mjs. Or you could source your env file using source .env && node .output/server/index.mjs.
Note that for a purely static site, it is not possible to set runtime configuration config after your project is prerendered.
If you want to use environment variables set at build time but do not care about updating these down the line (or only need to update them reactively within your app) then appConfig may be a better choice. You can define appConfig both within your nuxt.config (using environment variables) and also within an ~/app.config.ts file in your project.