env

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

Programming language: Go

License: MIT License

Tags: Configuration    

Latest version: v6.4.0

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/v6

The usage looks like this:

package main

import (
    "fmt"
    "time"

    "github.com/caarlos0/env/v6"
)

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" 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}

⚠️⚠️⚠️ Attention: unexported fields will be 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 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.

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.

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"`
}

Not Empty fields

While required demands the environment variable to be check, 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 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/v6"
)

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/v6"
)

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/v6"
)

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)
}

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/v6"
)

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{}
    if  err := Parse(&cfg, Options{
        Prefix: "T_",
        Environment: map[string]string{
            "T_FOO_HOME": "/foo",
            "T_BAR_HOME": "/bar",
            "T_BLAH":     "blahhh",
            "T_HOME":     "/clean",
        },
    }); err != nil {
        log.Fatal(err)
    }

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

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

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/v6"
)

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

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

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/v6"
)

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

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

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/v6"
)

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}
}

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