Load environment variables from .env or io.Reader in Go.

Put the gotenv package on your import statement:

import "github.com/subosito/gotenv"

To modify your app environment variables, gotenv expose 2 main functions:

• gotenv.Load
• gotenv.Apply

By default, gotenv.Load will look for a file called .env in the current working directory.

Behind the scene, it will then load .env file and export the valid variables to the environment variables. Make sure you call the method as soon as possible to ensure it loads all variables, say, put it on init() function.

Once loaded you can use os.Getenv() to get the value of the variable.

Let's say you have .env file:

APP_ID=1234567
APP_SECRET=abcdef

Here's the example of your app:

package main

import (
	"github.com/subosito/gotenv"
	"log"
	"os"
)

func init() {
	gotenv.Load()
}

func main() {
	log.Println(os.Getenv("APP_ID"))     // "1234567"
	log.Println(os.Getenv("APP_SECRET")) // "abcdef"
}

You can also load other than .env file if you wish. Just supply filenames when calling Load(). It will load them in order and the first value set for a variable will win.:

gotenv.Load(".env.production", "credentials")

While gotenv.Load loads entries from .env file, gotenv.Apply allows you to use any io.Reader:

gotenv.Apply(strings.NewReader("APP_ID=1234567"))

log.Println(os.Getenv("APP_ID"))
// Output: "1234567"

Both gotenv.Load and gotenv.Apply DO NOT overrides existing environment variables. If you want to override existing ones, you can see section below.

Besides above functions, gotenv also provides another functions that overrides existing:

• gotenv.OverLoad
• gotenv.OverApply

Here's the example of this overrides behavior:

os.Setenv("HELLO", "world")

// NOTE: using Apply existing value will be reserved
gotenv.Apply(strings.NewReader("HELLO=universe"))
fmt.Println(os.Getenv("HELLO"))
// Output: "world"

// NOTE: using OverApply existing value will be overridden
gotenv.OverApply(strings.NewReader("HELLO=universe"))
fmt.Println(os.Getenv("HELLO"))
// Output: "universe"

Both gotenv.Load and gotenv.OverLoad returns an error on something wrong occurred, like your env file is not exist, and so on. To make it easier to use, gotenv also provides gotenv.Must helper, to let it panic when an error returned.

err := gotenv.Load(".env-is-not-exist")
fmt.Println("error", err)
// error: open .env-is-not-exist: no such file or directory

gotenv.Must(gotenv.Load, ".env-is-not-exist")
// it will throw a panic
// panic: open .env-is-not-exist: no such file or directory

Just in case you want to parse environment variables from any io.Reader, gotenv keeps its Parse and StrictParse function as public API so you can use that.

// import "strings"

pairs := gotenv.Parse(strings.NewReader("FOO=test\nBAR=$FOO"))
// gotenv.Env{"FOO": "test", "BAR": "test"}

pairs, err := gotenv.StrictParse(strings.NewReader(`FOO="bar"`))
// gotenv.Env{"FOO": "bar"}

Parse ignores invalid lines and returns Env of valid environment variables, while StrictParse returns an error for invalid lines.

The gotenv package is a Go port of dotenv project with some additions made for Go. For general features, it aims to be compatible as close as possible.