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 "os" import "strings" import "fmt"
	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.Split` them to get the key and value. Here we print all the keys.	fmt.Println() for _, e := range os.Environ() { pair := strings.Split(e, "=") fmt.Println(pair[0]) } }

Running the program shows that we pick up the value value for `FOO` that we set in the program, but that `BAR` is empty.	$ go run environment-variables.go FOO: 1 BAR:
The list of keys in the environment will depend on your particular machine.	TERM_PROGRAM PATH SHELL ...
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 ...

Previous example: Command-Line Flags.