Environment Variables
In this lab, you will need to set, get, and list environment variables.
- Use
os.Setenv to set a key/value pair.
- Use
os.Getenv to get a value for a key.
- Use
os.Environ to list all key/value pairs in the environment.
- Use
strings.SplitN to split the key and value.
## 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
...
There is the full code below:
// [Environment variables](https://en.wikipedia.org/wiki/Environment_variable)
// are a universal mechanism for [conveying configuration
// information to Unix programs](https://www.12factor.net/config).
// 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])
}
}
