Interpolation

EnvGuard supports variable interpolation in .env files, allowing values to reference other variables.

Syntax

Use ${VAR} or $VAR to reference another variable:

BASE_URL=https://api.example.com
API_URL=${BASE_URL}/v1
FULL_URL=$BASE_URL/v2/resource

Default Values

Provide a default if the referenced variable is unset:

PORT=${APP_PORT:-3000}
HOST=${APP_HOST:-localhost}

Nested Interpolation

PROTOCOL=https
DOMAIN=example.com
BASE_URL=${PROTOCOL}://${DOMAIN}
API_URL=${BASE_URL}/api

Validation

EnvGuard resolves interpolations before validation:

# envguard.yaml
env:
  BASE_URL:
    type: string
    format: url
    required: true

  API_URL:
    type: string
    format: url
    required: true

# .env
BASE_URL=https://api.example.com
API_URL=${BASE_URL}/v1

$ envguard validate
✓ All environment variables are valid

Escaping

To include a literal $ in a value, use $$:

PRICE=$$100

Limitations

• Cyclic references are detected and rejected
• Interpolation only works within the same .env file
• Cross-file interpolation is not supported