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"`
    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"`
}

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