envconfig

import "github.com/kelseyhightower/envconfig"

Documentation

See godoc

Usage

Set some environment variables:

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 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"`
}

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 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 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

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"`
}

Also, envconfig will use a Set(string) error method like from the flag.Value interface if implemented.

Custom Getters

The Getter interface was added so that types that implement this can get values from places other than environment variables. An example would be to get values from consul, vault or some other store. The Getter will need to be implemented on the struct and this will override the EnvVar Getter. Example of custom getting:

type PluginTestGetter struct {
	EnvVarGetter

	SpecialValues map[string]map[string]string
}

// The Getter provider
func (g PluginTestGetter) Provider() string {
	return "PluginTestGetter"
}

func (t *PluginTestGetter) Get(key, alt string, tags reflect.StructTag) (string, bool, error) {
	special := tags.Get("special")
	if special != "" {
		var valueMap map[string]string
		var value string
		var exists bool
		valueMap, exists = t.SpecialValues[key]
		if exists {
			value, exists = valueMap[special]
			if exists {
				return value, true, nil
			}
		}
	}

	return t.EnvVarGetter.Get(key, alt, tags)
}

The example above will get values from a specified map if it a field has a particular map tag.