Get local IP with short subnet mask notation, example: "192.168.252.129/24"

getIPWithMask.go

package main

import (
	"fmt"
	"net"
	"os"
)

func getIPWithMask() string {
	addrs, err := net.InterfaceAddrs()
	if err != nil {
		os.Stderr.WriteString("Oops: " + err.Error() + "\n")
		os.Exit(1)
	}

	for _, a := range addrs {
		if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
			if ipnet.IP.To4() != nil {
				return ipnet.String()
			}
		}
	}

	return ""
}

func main() {
	fmt.Println(getIPWithMask())
}