Get Tailscale IP from terminal

main.go

package main

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

func main() {
	var ipv4 bool
	var ipv6 bool
	var all bool
	var up bool
	flag.BoolVar(&ipv4, "4", true, "print IPv4")
	flag.BoolVar(&ipv6, "6", false, "print IPv6")
	flag.BoolVar(&all, "all", false, "print IPv4 and IPv6")
	flag.BoolVar(&up, "up", true, "only print interfaces that are currently up")
	flag.Parse()

	if all {
		ipv4 = true
		ipv6 = true
	}

	interfaces, err := net.Interfaces()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error: %s\n", err)
		os.Exit(1)
	}
	for _, i := range interfaces {
		// Ignore hardware interfaces.
		if i.HardwareAddr != nil {
			continue
		}

		// Ignore interfaces that aren’t tunnels.
		if i.Flags&net.FlagPointToPoint == 0 {
			continue
		}

		// Ignore interfaces that are down.
		if up && i.Flags&net.FlagUp == 0 {
			continue
		}

		addrs, err := i.Addrs()
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error: %s\n", err)
			continue
		}

		for j, addr := range addrs {
			ipnet, ok := addr.(*net.IPNet)
			if !ok {
				fmt.Fprintf(os.Stderr, "Error: interface %s addr %d is not an IP network ", i.Name, j)
				continue
			}

			is4 := ipnet.IP.To4() != nil

			if (is4 && !ipv4) || (!is4 && !ipv6) {
				continue
			}

			fmt.Fprintf(os.Stderr, "Interface %s addr %d: ", i.Name, j)
			fmt.Print(ipnet.IP.String())
			fmt.Fprint(os.Stderr, "\n")
		}
	}
}

It only prints the IPs to stdout, so you can run go run main.go | pbcopy to get the Tailscale IPv4 address on the pasteboard.