envconfig

import "github.com/kelseyhightower/envconfig"

Documentation

See godoc

Usage

Set some environment variables (or define it in a .env file):

export MYAPP_DEBUG=false
export MYAPP_PORT=8080
export MYAPP_USER=Kelsey
export MYAPP_RATE="0.5"
export MYAPP_TIMEOUT="3m"
export MYAPP_USERS="rob,ken,robert"
export MYAPP_COLORCODES="red:1,green:2,blue:3"

Write some code:

package main

import (
    "fmt"
    "log"
    "time"

    "github.com/kelseyhightower/envconfig"
)

type Specification struct {
    Debug       bool
    Port        int
    User        string
    Users       []string
    Rate        float32
    Timeout     time.Duration
    ColorCodes  map[string]int
}

func main() {
    var s Specification
    err := envconfig.Process("myapp", &s)

    // if reading from a .env file
    // err := envoconfig.ProcessFromFile("/fully/qualified/path/to/.env", "myapp", &s)

    if err != nil {
        log.Fatal(err.Error())
    }
    format := "Debug: %v\nPort: %d\nUser: %s\nRate: %f\nTimeout: %s\n"
    _, err = fmt.Printf(format, s.Debug, s.Port, s.User, s.Rate, s.Timeout)
    if err != nil {
        log.Fatal(err.Error())
    }

    fmt.Println("Users:")
    for _, u := range s.Users {
        fmt.Printf("  %s\n", u)
    }

    fmt.Println("Color codes:")
    for k, v := range s.ColorCodes {
        fmt.Printf("  %s: %d\n", k, v)
    }
}

Results:

Debug: false
Port: 8080
User: Kelsey
Rate: 0.500000
Timeout: 3m0s
Users:
  rob
  ken
  robert
Color codes:
  red: 1
  green: 2
  blue: 3

Struct Tag Support

Envconfig supports the use of struct tags to specify alternate, default, and required environment variables.

For example, consider the following struct:

type Specification struct {
    ManualOverride1 string `envconfig:"manual_override_1"`
    DefaultVar      string `default:"foobar"`
    RequiredVar     string `required:"true"`
    IgnoredVar      string `ignored:"true"`
    AutoSplitVar    string `split_words:"true"`
    RequiredAndAutoSplitVar    string `required:"true" split_words:"true"`
}

Envconfig has automatic support for CamelCased struct elements when the split_words:"true" tag is supplied. Without this tag, AutoSplitVar above would look for an environment variable called MYAPP_AUTOSPLITVAR. With the setting applied it will look for MYAPP_AUTO_SPLIT_VAR. Note that numbers will get globbed into the previous word. If the setting does not do the right thing, you may use a manual override.

Envconfig will process value for ManualOverride1 by populating it with the value for MYAPP_MANUAL_OVERRIDE_1. Without this struct tag, it would have instead looked up MYAPP_MANUALOVERRIDE1. With the split_words:"true" tag it would have looked up MYAPP_MANUAL_OVERRIDE1.

export MYAPP_MANUAL_OVERRIDE_1="this will be the value"

# export MYAPP_MANUALOVERRIDE1="and this will not"

If envconfig can't find an environment variable value for MYAPP_DEFAULTVAR, it will populate it with "foobar" as a default value.

If envconfig can't find an environment variable value for MYAPP_REQUIREDVAR, it will return an error when asked to process the struct. If MYAPP_REQUIREDVAR is present but empty, envconfig will not return an error.

If envconfig can't find an environment variable in the form PREFIX_MYVAR, and there is a struct tag defined, it will try to populate your variable with an environment variable that directly matches the envconfig tag in your struct definition:

export SERVICE_HOST=127.0.0.1
export MYAPP_DEBUG=true

type Specification struct {
    ServiceHost string `envconfig:"SERVICE_HOST"`
    Debug       bool
}

Envconfig won't process a field with the "ignored" tag set to "true", even if a corresponding environment variable is set.

Supported Struct Field Types

envconfig supports these struct field types:

string
int8, int16, int32, int64
bool
float32, float64
slices of any supported type
maps (keys and values of any supported type)
encoding.TextUnmarshaler
encoding.BinaryUnmarshaler
time.Duration

Embedded structs using these fields are also supported.

Custom Decoders

Any field whose type (or pointer-to-type) implements envconfig.Decoder can control its own deserialization:

export DNS_SERVER=8.8.8.8

type IPDecoder net.IP

func (ipd *IPDecoder) Decode(value string) error {
    *ipd = IPDecoder(net.ParseIP(value))
    return nil
}

type DNSConfig struct {
    Address IPDecoder `envconfig:"DNS_SERVER"`
}

Example for decoding the environment variables into map[string][]structName type

export SMS_PROVIDER_WITH_WEIGHT= `IND=[{"name":"SMSProvider1","weight":70},{"name":"SMSProvider2","weight":30}];US=[{"name":"SMSProvider1","weight":100}]`

type providerDetails struct {
	Name   string
	Weight int
}

type SMSProviderDecoder map[string][]providerDetails

func (sd *SMSProviderDecoder) Decode(value string) error {
	smsProvider := map[string][]providerDetails{}
	pairs := strings.Split(value, ";")
	for _, pair := range pairs {
		providerdata := []providerDetails{}
		kvpair := strings.Split(pair, "=")
		if len(kvpair) != 2 {
			return fmt.Errorf("invalid map item: %q", pair)
		}
		err := json.Unmarshal([]byte(kvpair[1]), &providerdata)
		if err != nil {
			return fmt.Errorf("invalid map json: %w", err)
		}
		smsProvider[kvpair[0]] = providerdata

	}
	*sd = SMSProviderDecoder(smsProvider)
	return nil
}

type SMSProviderConfig struct {
    ProviderWithWeight SMSProviderDecoder `envconfig:"SMS_PROVIDER_WITH_WEIGHT"`
}