Go by Example: Environment Variables

Environment variables are a universal mechanism for conveying configuration information to Unix programs. Let’s look at how to set, get, and list environment variables.

package main
import (
func main() {

To set a key/value pair, use os.Setenv. To get a value for a key, use os.Getenv. This will return an empty string if the key isn’t present in the environment.

    os.Setenv("FOO", "1")
    fmt.Println("FOO:", os.Getenv("FOO"))
    fmt.Println("BAR:", os.Getenv("BAR"))

Use os.Environ to list all key/value pairs in the environment. This returns a slice of strings in the form KEY=value. You can strings.SplitN them to get the key and value. Here we print all the keys.

    for _, e := range os.Environ() {
        pair := strings.SplitN(e, "=", 2)

Running the program shows that we pick up the value for FOO that we set in the program, but that BAR is empty.

$ go run environment-variables.go
FOO: 1

The list of keys in the environment will depend on your particular machine.


If we set BAR in the environment first, the running program picks that value up.

$ BAR=2 go run environment-variables.go
FOO: 1
BAR: 2

Next example: Logging.