env

env is an environment variable utility package for Go. It provides simple functions to get and set environment variables, including support for unmarshalling environment variables into structs with support for nested structures, default values, and required fields.

Features

• Basic Get/Set: Simple functions to get, set, and unset environment variables.
• Type Conversion: Functions to get environment variables as different types (int, bool, float).
• Fallback Values: Support for fallback values if an environment variable is not set.
• Unmarshal: Load environment variables into structs using struct tags.
• Nested Structs: Support for nested struct prefixes to group environment variables.

Installation

go get github.com/syntaqx/env

Basic Usage

package main

import (
    "fmt"
    "github.com/syntaqx/env"
)

func main() {
    port := env.GetWithFallback("PORT", "8080")
    fmt.Printf("Port: %s\n", port)

    // Assuming the value of HOSTS is a comma-separated list of strings
    // Example: some-host:8000,another-host:8000
    hosts, err := env.GetStringSliceWithFallback("HOSTS", []string{"fallback-host-1:8000", "fallback-host-2:8000"})
    if err != nil {
        fmt.Printf("Error getting hosts: %v\n", err)
    } else {
        fmt.Printf("Hosts: %v\n", hosts)
    }
}

Unmarshal to Struct

The Unmarshal function allows you to load environment variables into a struct based on struct tags. You can use default or fallback for fallback values and required to enforce that an environment variable must be set.

package main

import (
    "fmt"
    "log"

    "github.com/syntaqx/env"
)

type DatabaseConfig struct {
    Host     string `env:"DATABASE_HOST,default=localhost"`
    Port     int    `env:"DATABASE_PORT|DB_PORT,fallback=3306"`
    Username string `env:"DATABASE_USERNAME,default=root"`
    Password string `env:"DATABASE_PASSWORD,required"`
    Database string `env:"DATABASE_NAME"`
}

type Config struct {
    Debug    bool           `env:"DEBUG"`
    Port     string         `env:"PORT,default=8080"`
    Database DatabaseConfig
}

func main() {
    var cfg Config

    // Set example environment variables
    _ = env.Set("DEBUG", "true")
    _ = env.Set("PORT", "9090")
    _ = env.Set("DATABASE_HOST", "dbhost")
    _ = env.Set("DATABASE_PORT", "5432")
    _ = env.Set("DATABASE_USERNAME", "admin")
    _ = env.Set("DATABASE_PASSWORD", "secret")
    _ = env.Set("DATABASE_NAME", "mydb")

    if err := env.Unmarshal(&cfg); err != nil {
        log.Fatalf("Error unmarshalling config: %v", err)
    }

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

Nested Struct Prefixes

You can use nested prefixes to group environment variables. This allows you to reuse the same struct in multiple places without having to worry about conflicting environment variables.

package main

import (
    "fmt"
    "log"

    "github.com/syntaqx/env"
)

type DatabaseConfig struct {
    Host     string `env:"HOST,default=localhost"`
    Port     int    `env:"PORT,fallback=3306"`
    Username string `env:"USERNAME,default=root"`
    Password string `env:"PASSWORD,required"`
    Database string `env:"NAME"`
}

type Config struct {
    Debug         bool           `env:"DEBUG"`
    Port          string         `env:"PORT,default=8080"`
    ReadDatabase  DatabaseConfig `env:"READ_DATABASE"`
    WriteDatabase DatabaseConfig `env:"WRITE_DATABASE"`
}

func main() {
    var cfg Config

    // Set example environment variables
    _ = env.Set("DEBUG", "true")
    _ = env.Set("PORT", "9090")
    _ = env.Set("READ_DATABASE_HOST", "read-dbhost")
    _ = env.Set("READ_DATABASE_PORT", "5432")
    _ = env.Set("READ_DATABASE_USERNAME", "read-admin")
    _ = env.Set("READ_DATABASE_PASSWORD", "read-secret")
    _ = env.Set("READ_DATABASE_NAME", "read-mydb")
    _ = env.Set("WRITE_DATABASE_HOST", "write-dbhost")
    _ = env.Set("WRITE_DATABASE_PORT", "5432")
    _ = env.Set("WRITE_DATABASE_USERNAME", "write-admin")
    _ = env.Set("WRITE_DATABASE_PASSWORD", "write-secret")
    _ = env.Set("WRITE_DATABASE_NAME", "write-mydb")

    if err := env.Unmarshal(&cfg); err != nil {
        log.Fatalf("Error unmarshalling config: %v", err)
    }

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

Slice Types Defaults

When using slice types, if you are declaring a single value as the default you can use the default tag as normal:

type Config struct {
	Hosts []string `env:"HOSTS,default=localhost"`
}

However if you want to declare multiple values as the default, you must enclose the values in square brackets:

type Config struct {
	Hosts []string `env:"HOSTS,default=[localhost,localhost2]`
}

This is necessary as the pacakge uses commas as a delimiter to split the struct tag options, and without the square brackets it would split the values into multiple tags.

type Config struct {
	Hosts []string `env:"HOSTS,default=[localhost,localhost2],required"
}

Defaults from Code

You may define default values also in your code by initializing your struct data before it's populated by env.Unmarshal. However, default values defined as struct tags will take precedence over the ones defined in code.

type Config struct {
    Username string `env:"USERNAME,default=admin"`
    Password string `env:"PASSWORD"`
}

cfg := Config{
    Username: "test",
    Password: "password123",
}

if err := env.Unmarshal(&cfg); err != nil {
    log.Fatalf("Error unmarshalling config: %v", err)
}

// { Username: "admin", Password: "password123" }

From file

The file tag option can be used to indicate that the value of the variable should be loaded from a file. The path of the file given by the value of the variable.

echo "password123" > /run/secrets/password

type Config struct {
    Username string `env:"USERNAME"`
    Password string `env:"PASSWORD,file"`
}

cfg := Config{
    Username: "test",
    Password: "/run/secrets/password",
}

if err := env.Unmarshal(&cfg); err != nil {
    log.Fatalf("Error unmarshalling config: %v", err)
}

// { "Username": "test", "Password": "password123" }

Expand variables

The expand tag option can be used to indicate that the value of the variable should be expanded (in either ${var} or $var format) before being set.

type Config struct {
    Username string `env:"USERNAME,expand"`
    Password string `env:"PASSWORD,expand"`
}

This works great with the default tag option:

type Config struct {
    Address string `env:"ADDRESS,expand,default=${HOST}:${PORT}"`
}

Which results in:

HOST=localhost PORT=8080 go run main.go
{Address:localhost:8080}

Additionally, default values can be referenced from other struct fields. Allowing you to chain default values rather than falling back to an empty value when an environment variable is not set:

type Config struct {
    Host string `env:"HOST,default=localhost"`
    Port string `env:"PORT,default=8080"`
    Address string `env:"ADDRESS,expand,default=${HOST}:${PORT}"`
}

Which results in:

go run main.go
{Host:localhost Port:8080 Address:localhost:8080}

Contributing

Feel free to open issues or contribute to the project. Contributions are always welcome!

License

This project is licensed under the MIT license.