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 (
    "fmt"
    "os"
    "strings"
)

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.
    fmt.Println()
    for _, e := range os.Environ() {
        pair := strings.SplitN(e, "=", 2)
        fmt.Println(pair[0])
    }
}

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

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.

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

TERM_PROGRAM
PATH
SHELL
...
FOO

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