### [Read this on the main serverless docs site](https://www.serverless.com/framework/docs/providers/knative/guide/variables/) # Knative Variables Variables allow users to dynamically replace config values in `serverless.yml` config. They are especially useful when providing secrets for your service to use and when you are working with multiple stages. The Serverless Framework provides a powerful variable system which allows you to add dynamic data into your `serverless.yml`. With Serverless Variables, you'll be able to do the following: - Reference & load variables from environment variables via `${env:FOO}` - Reference & load variables from CLI options via `${opt:stage}` - Recursively reference properties of any type from the same `serverless.yml` file via `${self:provider.name}` - Recursively reference properties of any type from other YAML / JSON files via `${file(./some-file.json):exportedVar}` - Recursively nest variable references within each other for ultimate flexibility - Combine multiple variable references to overwrite each other **Note:** You can only use variables in `serverless.yml` property **values**, not property keys. So you can't use variables to generate dynamic logical IDs in the custom resources section for example.