env

README

env

A simple and zero-dependencies library to parse environment variables into structs.

Example

Get the module with:

go get github.com/caarlos0/env/v9

The usage looks like this:

package main

import (
	"fmt"
	"time"

	"github.com/caarlos0/env/v9"
)

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

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}

Caveats

Warning

This is important!

• Unexported fields are ignored

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
• time.Duration
• encoding.TextUnmarshaler
• url.URL

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

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

You can also use custom keys and values in your maps, as long as you provide a parser function for them.

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.

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.ParseWithOptions() function.

In addition to accepting a struct pointer (same as Parse()), this function also accepts a Options{}, and you can set your custom parsers in the FuncMap field.

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

Check the examples in the go doc for more info.

A note about TextUnmarshaler and time.Time

Env supports by default anything that implements the TextUnmarshaler interface. That includes things like time.Time for example. The upside is that depending on the format you need, you don't need to change anything. The downside is that if you do need time in another format, you'll need to create your own type.

Its fairly straightforward:

type MyTime time.Time

func (t *MyTime) UnmarshalText(text []byte) error {
	tt, err := time.Parse("2006-01-02", string(text))
	*t = MyTime(tt)
	return err
}

type Config struct {
	SomeTime MyTime `env:"SOME_TIME"`
}

And then you can parse Config with env.Parse.

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 {
	SecretKey string `env:"SECRET_KEY,required"`
}

Warning

Note that being set is not the same as being empty. If the variable is set, but empty, the field will have its type's default value. This also means that custom parser funcs will not be invoked.

Expand vars

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

type config struct {
	SecretKey string `env:"SECRET_KEY,expand"`
}

This also works with envDefault.

Not Empty fields

While required demands the environment variable to be set, it doesn't check its value. If you want to make sure the environment is set and not empty, you need to use the notEmpty tag option instead (env:"SOME_ENV,notEmpty").

Example:

type config struct {
	SecretKey string `env:"SECRET_KEY,notEmpty"`
}

Unset environment variable after reading it

The env tag option unset (e.g., env:"tagKey,unset") can be added to ensure that some environment variable is unset after reading it.

Example:

type config struct {
	SecretKey string `env:"SECRET_KEY,unset"`
}

From file

The env tag option file (e.g., env:"tagKey,file") can be added 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:

package main

import (
	"fmt"
	"time"
	"github.com/caarlos0/env/v9"
)

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

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

Use field names as environment variables by default

If you don't want to set the env tag on every field, you can use the UseFieldNameByDefault option.

It will use the field name as environment variable name.

Here's an example:

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env/v9"
)

type Config struct {
	Username     string // will use $USERNAME
	Password     string // will use $PASSWORD
	UserFullName string // will use $USER_FULL_NAME
}

func main() {
	cfg := &Config{}
	opts := env.Options{UseFieldNameByDefault: true}

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

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

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/v9"
)

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.ParseWithOptions(cfg, opts); err != nil {
		log.Fatal(err)
	}

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

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/v9"
)

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

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

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

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

Prefixes

You can prefix sub-structs env tags, as well as a whole env.Parse call.

Here's an example flexing it a bit:

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env/v9"
)

type Config struct {
	Home string `env:"HOME"`
}

type ComplexConfig struct {
	Foo   Config `envPrefix:"FOO_"`
	Clean Config
	Bar   Config `envPrefix:"BAR_"`
	Blah  string `env:"BLAH"`
}

func main() {
	cfg := &ComplexConfig{}
	opts := env.Options{
		Prefix: "T_",
		Environment: map[string]string{
			"T_FOO_HOME": "/foo",
			"T_BAR_HOME": "/bar",
			"T_BLAH":     "blahhh",
			"T_HOME":     "/clean",
		},
	}

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

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

On set hooks

You might want to listen to value sets and, for example, log something or do some other kind of logic. You can do this by passing a OnSet option:

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env/v9"
)

type Config struct {
	Username string `env:"USERNAME" envDefault:"admin"`
	Password string `env:"PASSWORD"`
}

func main() {
	cfg := &Config{}
	opts := env.Options{
		OnSet: func(tag string, value interface{}, isDefault bool) {
			fmt.Printf("Set %s to %v (default? %v)\n", tag, value, isDefault)
		},
	}

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

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

Making all fields to required

You can make all fields that don't have a default value be required by setting the RequiredIfNoDef: true in the Options.

For example

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env/v9"
)

type Config struct {
	Username string `env:"USERNAME" envDefault:"admin"`
	Password string `env:"PASSWORD"`
}

func main() {
	cfg := &Config{}
	opts := env.Options{RequiredIfNoDef: true}

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

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

Defaults from code

You may define default value also in code, by initialising the config data before it's filled by env.Parse. Default values defined as struct tags will overwrite existing values during Parse.

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env/v9"
)

type Config struct {
	Username string `env:"USERNAME" envDefault:"admin"`
	Password string `env:"PASSWORD"`
}

func main() {
	var cfg = Config{
		Username: "test",
		Password: "123456",
	}

	if err := env.Parse(&cfg); err != nil {
		fmt.Println("failed:", err)
	}

	fmt.Printf("%+v", cfg)  // {Username:admin Password:123456}
}

Error handling

You can handle the errors the library throws like so:

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env/v9"
)

type Config struct {
	Username string `env:"USERNAME" envDefault:"admin"`
	Password string `env:"PASSWORD"`
}

func main() {
	var cfg Config
	err := env.Parse(&cfg)
	if e, ok := err.(*env.AggregateError); ok {
		for _, er := range e.Errors {
			switch v := er.(type) {
			case env.ParseError:
				// handle it
			case env.NotStructPtrError:
				// handle it
			case env.NoParserError:
				// handle it
			case env.NoSupportedTagOptionError:
				// handle it
			default:
				fmt.Printf("Unknown error type %v", v)
			}
		}
	}

	fmt.Printf("%+v", cfg)  // {Username:admin Password:123456}
}

Info

If you want to check if an specific error is in the chain, you can also use errors.Is().

Stargazers over time

Documentation

Index

• func Parse(v interface{}) error
• func ParseWithOptions(v interface{}, opts Options) error
• type AggregateError
  • func (e AggregateError) Error() string
  • func (e AggregateError) Is(err error) bool
• type EmptyEnvVarError
  • func (e EmptyEnvVarError) Error() string
• type EnvVarIsNotSetError
  • func (e EnvVarIsNotSetError) Error() string
• type LoadFileContentError
  • func (e LoadFileContentError) Error() string
• type NoParserError
  • func (e NoParserError) Error() string
• type NoSupportedTagOptionError
  • func (e NoSupportedTagOptionError) Error() string
• type NotStructPtrError
  • func (e NotStructPtrError) Error() string
• type OnSetFn
• type Options
• type ParseError
  • func (e ParseError) Error() string
• type ParseValueError
  • func (e ParseValueError) Error() string
• type ParserFunc

Examples

• Parse
• Parse (Defaults)
• Parse (OnSet)
• ParseWithOptions

Functions

func Parse

func Parse(v interface{}) error

Parse parses a struct containing `env` tags and loads its values from environment variables.

Example

type inner struct {
	Foo string `env:"FOO" envDefault:"foobar"`
}
type config struct {
	Home         string `env:"HOME,required"`
	Port         int    `env:"PORT" envDefault:"3000"`
	IsProduction bool   `env:"PRODUCTION"`
	TempFolder   string `env:"TEMP_FOLDER,expand" envDefault:"${HOME}/.tmp"`
	Inner        inner
}
os.Setenv("HOME", "/tmp/fakehome")
var cfg config
if err := Parse(&cfg); err != nil {
	fmt.Println("failed:", err)
}
fmt.Printf("%+v", cfg)

Output:

{Home:/tmp/fakehome Port:3000 IsProduction:false TempFolder:/tmp/fakehome/.tmp Inner:{Foo:foobar}}

Example (Defaults)

type config struct {
	A string `env:"FOO" envDefault:"foo"`
	B string `env:"FOO"`
}

// env FOO is not set

cfg := config{
	A: "A",
	B: "B",
}
if err := Parse(&cfg); err != nil {
	fmt.Println("failed:", err)
}
fmt.Printf("%+v", cfg)

Output:

{A:foo B:B}

Example (OnSet)

type config struct {
	Home         string `env:"HOME,required"`
	Port         int    `env:"PORT" envDefault:"3000"`
	IsProduction bool   `env:"PRODUCTION"`
	NoEnvTag     bool
	Inner        struct{} `envPrefix:"INNER_"`
}
os.Setenv("HOME", "/tmp/fakehome")
var cfg config
if err := ParseWithOptions(&cfg, Options{
	OnSet: func(tag string, value interface{}, isDefault bool) {
		fmt.Printf("Set %s to %v (default? %v)\n", tag, value, isDefault)
	},
}); err != nil {
	fmt.Println("failed:", err)
}
fmt.Printf("%+v", cfg)

Output:

Set HOME to /tmp/fakehome (default? false)
Set PORT to 3000 (default? true)
Set PRODUCTION to  (default? false)
{Home:/tmp/fakehome Port:3000 IsProduction:false NoEnvTag:false Inner:{}}

func ParseWithOptions

func ParseWithOptions(v interface{}, opts Options) error

Parse parses a struct containing `env` tags and loads its values from environment variables.

Example

type thing struct {
	desc string
}

type conf struct {
	Thing thing `env:"THING"`
}

os.Setenv("THING", "my thing")

c := conf{}

err := ParseWithOptions(&c, Options{FuncMap: map[reflect.Type]ParserFunc{
	reflect.TypeOf(thing{}): func(v string) (interface{}, error) {
		return thing{desc: v}, nil
	},
}})
if err != nil {
	fmt.Println(err)
}
fmt.Println(c.Thing.desc)

Output:

my thing

Types

type AggregateError

type AggregateError struct {
	Errors []error
}

An aggregated error wrapper to combine gathered errors. This allows either to display all errors or convert them individually List of the available errors ParseError NotStructPtrError NoParserError NoSupportedTagOptionError EnvVarIsNotSetError EmptyEnvVarError LoadFileContentError ParseValueError

func (AggregateError) Error

func (e AggregateError) Error() string

func (AggregateError) Is

func (e AggregateError) Is(err error) bool

Is conforms with errors.Is.

type EmptyEnvVarError

type EmptyEnvVarError struct {
	Key string
}

This error occurs when the variable which must be not empty is existing but has an empty value Read about not empty fields: https://github.com/caarlos0/env#not-empty-fields

func (EmptyEnvVarError) Error

func (e EmptyEnvVarError) Error() string

type EnvVarIsNotSetError

type EnvVarIsNotSetError struct {
	Key string
}

This error occurs when the required variable is not set Read about required fields: https://github.com/caarlos0/env#required-fields

func (EnvVarIsNotSetError) Error

func (e EnvVarIsNotSetError) Error() string

type LoadFileContentError

type LoadFileContentError struct {
	Filename string
	Key      string
	Err      error
}

This error occurs when it's impossible to load the value from the file Read about From file feature: https://github.com/caarlos0/env#from-file

func (LoadFileContentError) Error

func (e LoadFileContentError) Error() string

type NoParserError

type NoParserError struct {
	Name string
	Type reflect.Type
}

This error occurs when there is no parser provided for given type Supported types and defaults: https://github.com/caarlos0/env#supported-types-and-defaults How to create a custom parser: https://github.com/caarlos0/env#custom-parser-funcs

func (NoParserError) Error

func (e NoParserError) Error() string

type NoSupportedTagOptionError

type NoSupportedTagOptionError struct {
	Tag string
}

This error occurs when the given tag is not supported In-built supported tags: "", "file", "required", "unset", "notEmpty", "expand", "envDefault", "envSeparator" How to create a custom tag: https://github.com/caarlos0/env#changing-default-tag-name

func (NoSupportedTagOptionError) Error

func (e NoSupportedTagOptionError) Error() string

type NotStructPtrError

type NotStructPtrError struct{}

The error occurs when pass something that is not a pointer to a Struct to Parse

func (NotStructPtrError) Error

func (e NotStructPtrError) Error() string

type OnSetFn

type OnSetFn func(tag string, value interface{}, isDefault bool)

OnSetFn is a hook that can be run when a value is set.

type Options

type Options struct {
	// Environment keys and values that will be accessible for the service.
	Environment map[string]string

	// TagName specifies another tagname to use rather than the default env.
	TagName string

	// RequiredIfNoDef automatically sets all env as required if they do not
	// declare 'envDefault'.
	RequiredIfNoDef bool

	// OnSet allows to run a function when a value is set.
	OnSet OnSetFn

	// Prefix define a prefix for each key.
	Prefix string

	// UseFieldNameByDefault defines whether or not env should use the field
	// name by default if the `env` key is missing.
	UseFieldNameByDefault bool

	// Custom parse functions for different types.
	FuncMap map[reflect.Type]ParserFunc
}

Options for the parser.

type ParseError

type ParseError struct {
	Name string
	Type reflect.Type
	Err  error
}

The error occurs when it's impossible to convert the value for given type.

func (ParseError) Error

func (e ParseError) Error() string

type ParseValueError

type ParseValueError struct {
	Msg string
	Err error
}

This error occurs when it's impossible to convert value using given parser Supported types and defaults: https://github.com/caarlos0/env#supported-types-and-defaults How to create a custom parser: https://github.com/caarlos0/env#custom-parser-funcs

func (ParseValueError) Error

func (e ParseValueError) Error() string

type ParserFunc

type ParserFunc func(v string) (interface{}, error)

ParserFunc defines the signature of a function that can be used within `CustomParsers`.