Programming language: Go
Tags: Configuration    
Latest version: v6.0.0

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Simple lib to parse envs to structs in Go.


A very basic example:

package main

import (

  // if using go modules

  // if using dep/others

type config struct {
    Home         string        `env:"HOME"`
    Port         int           `env:"PORT" envDefault:"3000"`
    IsProduction bool          `env:"PRODUCTION"`
    Hosts        []string      `env:"HOSTS" envSeparator:":"`
    Duration     time.Duration `env:"DURATION"`
    TempFolder   string        `env:"TEMP_FOLDER" envDefault:"${HOME}/tmp" envExpand:"true"`

func main() {
    cfg := config{}
    if err := env.Parse(&cfg); err != nil {
        fmt.Printf("%+v\n", err)

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

You can run it like this:

$ PRODUCTION=true HOSTS="host1:host2:host3" DURATION=1s go run main.go
{Home:/your/home Port:3000 IsProduction:true Hosts:[host1 host2 host3] Duration:1s}

Supported types and defaults

Out of the box all built-in types are supported, plus a few others that are commonly used.

Complete list:

  • string
  • bool
  • int
  • int8
  • int16
  • int32
  • int64
  • uint
  • uint8
  • uint16
  • uint32
  • uint64
  • float32
  • float64
  • string
  • time.Duration
  • encoding.TextUnmarshaler
  • url.URL

Pointers, slices and slices of pointers of those types are also supported.

You can also use/define a custom parser func for any other type you want.

If you set the envDefault tag for something, this value will be used in the case of absence of it in the environment.

By default, slice types will split the environment value on ,; you can change this behavior by setting the envSeparator tag.

If you set the envExpand tag, environment variables (either in ${var} or $var format) in the string will be replaced according with the actual value of the variable.

Unexported fields are ignored.

Custom Parser Funcs

If you have a type that is not supported out of the box by the lib, you are able to use (or define) and pass custom parsers (and their associated reflect.Type) to the env.ParseWithFuncs() function.

In addition to accepting a struct pointer (same as Parse()), this function also accepts a map[reflect.Type]env.ParserFunc.

env also ships with some pre-built custom parser funcs for common types. You can check them out [here](parsers/).

If you add a custom parser for, say Foo, it will also be used to parse *Foo and []Foo types.

This directory contains pre-built, custom parsers that can be used with env.ParseWithFuncs to facilitate the parsing of envs that are not basic types.

Check the example in the go doc for more info.

Required fields

The env tag option required (e.g., env:"tagKey,required") can be added to ensure that some environment variable is set. In the example above, an error is returned if the config struct is changed to:

type config struct {
    Home         string   `env:"HOME"`
    Port         int      `env:"PORT" envDefault:"3000"`
    IsProduction bool     `env:"PRODUCTION"`
    Hosts        []string `env:"HOSTS" envSeparator:":"`
    SecretKey    string   `env:"SECRET_KEY,required"`

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