Master Golang: 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.

 
$ 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
...
FOO

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: HTTP Client.

Gratitude to Mark McGranaghan and Eli Bendersky