env

Simple lib to parse envs to structs in Go.

Example

A very basic example:

package main

import (
	"fmt"
	"time"

	// if using go modules
	"github.com/caarlos0/env/v6"

	// if using dep/others
	"github.com/caarlos0/env"
)

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.

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"`
}

From file

The env tag option file (e.g., env:"tagKey,file") can be added to in order to indicate that the value of the variable shall be loaded from a file. The path of that file is given by the environment variable associated with it Example below

package main

import (
	"fmt"
	"time"
	"github.com/caarlos0/env"
)

type config struct {
	Secret       string   `env:"SECRET,file"`
	Password     string   `env:"PASSWORD,file" envDefault:"/tmp/password"`
	Certificate  string   `env:"CERTIFICATE,file" envDefault:"${CERTIFICATE_FILE}" envExpand:"true"`
}

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

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

$ echo qwerty > /tmp/secret
$ echo dvorak > /tmp/password
$ echo coleman > /tmp/certificate

$ SECRET=/tmp/secret  \
	CERTIFICATE_FILE=/tmp/certificate \
	go run main.go
{Secret:qwerty Password:dvorak Certificate:coleman}

Options

Environment

By setting the Options.Environment map you can tell Parse to add those keys and values as env vars before parsing is done. These envs are stored in the map and never actually set by os.Setenv. This option effectively makes env ignore the OS environment variables: only the ones provided in the option are used.

This can make your testing scenarios a bit more clean and easy to handle.

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env"
)

type Config struct {
	Password string `env:"PASSWORD"`
}

func main() {
	cfg := &Config{}
	opts := &env.Options{Environment: map[string]string{
		"PASSWORD": "MY_PASSWORD",
	}}

	// Load env vars.
	if err := env.Parse(cfg, opts); err != nil {
		log.Fatal(err)
	}

	// Print the loaded data.
	fmt.Printf("%+v\n", cfg.envData)
}

Changing default tag name

You can change what tag name to use for setting the env vars by setting the Options.TagName variable.

For example

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env"
)

type Config struct {
	Password string `json:"PASSWORD"`
}

func main() {
	cfg := &Config{}
	opts := &env.Options{TagName: "json"}

	// Load env vars.
	if err := env.Parse(cfg, opts); err != nil {
		log.Fatal(err)
	}

	// Print the loaded data.
	fmt.Printf("%+v\n", cfg.envData)
}

mohsensamiei/env

env