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Generating .env.example

A common need when using environment variables is to provide a .env.example file that shows developers what variables they need to set up. With envoyage, you can automatically generate this file using the listVariables method.

The Pattern​

Let's say you have a "local" environment that uses the "from-env" resolution to read variables from a .env file:

const envReg = createEnvironmentRegistry()
  .addEnv("local", /* ... */, (e) => e
    .addResolution("from-env", /* ... */)
  .addEnv(/* ... */)

You can generate a .env.example file by listing all variables that use the "from-env" resolution in the "local" environment:

// Get all variables that use "from-env" in the local environment
const localEnvVars = varReg.listVariables("local", "from-env")
// Returns: ["DATABASE_URL", "REDIS_URL", "API_KEY"]

// Generate .env.example content
const envExample = localEnvVars
  .map(key => `${key}=`)
  .join("\n")

// Write to file
fs.writeFileSync(".env.example", envExample)

This will create a .env.example file like:

DATABASE_URL=
REDIS_URL=
API_KEY=

Why This Works​

The listVariables method is designed to find all variables that use a specific resolution method in a target environment. In this case:

  1. We ask for all variables that use "from-env" in the "local" environment
  2. The method returns an array of variable names
  3. We can use this to generate our example file

This pattern ensures that your .env.example stays in sync with your codebase, as it's generated directly from your variable definitions.