envsubst

A lightweight Go package for substituting environment variables in configuration strings, similar to Docker Compose's ${VAR} syntax.

Features

• ✅ Replaces ${VAR} with the value of the corresponding environment variable
• ❌ Does not yet support default values (${VAR:-default}) or required checks (${VAR:?error}) — coming soon!

Installation

go get github.com/emperorsixpacks/envsubst

Usage

import (
	"fmt"
	"os"

	"github.com/emperorsixpacks/envsubst"
)

type Config struct {
	Name    string   `yaml:"name"`
	Version string   `yaml:"version"`
	Port    []int    `yaml:"port"`
	Network string   `yaml:"network"`
}

func main() {
	os.Setenv("CLIENT_NAME", "lighthouse")
	yml := []byte(`
name: ${CLIENT_NAME}
version: v1.2.3
port:
  - 30303
  - 8545
network: testnet
`)

	var cfg Config
	if err := envsubst.Unmarshal(yml, &cfg); err != nil {
		panic(err)
	}

	fmt.Printf("%+v\n", cfg)
}