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    Go by Example: Environment Variables

    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 (
    "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: Logging .

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