02-environment

Example 02: Environment Variables

Loading configuration from environment variables with prefix handling.

What This Shows

• Using FromEnv to load environment variables
• Prefix stripping (MYAPP_ prefix is removed during matching)
• Layer precedence (environment overrides defaults)
• How non-prefixed variables are ignored

Running

go run main.go

Key Points

1. FromEnv - Creates a layer from environment variables
2. Prefix Stripping - MYAPP_SERVER_PORT matches server.port
3. Precedence - Later layers (environment) override earlier ones (defaults)
4. Selective Loading - Only variables with the prefix are included

Environment Variable Matching

The library automatically matches environment variables to configuration keys:

• MYAPP_SERVER_PORT → server.port
• MYAPP_DATABASE_HOST → database.host
• MYAPP_FEATURE_BETA → feature.beta

Output Example

=== Layer Contents ===

Layer: defaults (prefix: "")
  server.port = 8080
  server.host = localhost
  database.host = localhost
  ...

Layer: environment (prefix: "MYAPP_")
  MYAPP_SERVER_PORT = 9000
  MYAPP_DATABASE_HOST = db.production.com
  ...

=== Resolved Configuration ===
server.port          = 9000                (from environment)
server.host          = localhost           (from defaults)
database.host        = db.production.com   (from environment)
...