GO : ssh into Unix get users /etc/passwd and finding groups associated for every user

I am new to Golang. I am able to get the list of users from cat /etc/passwd. What I am trying to achieve is that for every user returned by cat /etc/passwd, I want to run the "id -user" command and map the user groups to that user. What data structure should I use? OR

Is there a Shell command that I can get fire to achieve the above?
I tried this -

for user in $(awk -F: '{print $1}' /etc/passwd); do groups $user; done

AND

tail -n +1 -F /etc/passwd | head -n +2500 -f":" /etc/passwd

> What data structure should I use?

You could use anything from arrays, lists, maps, dictionaries, to anything, there are no specific constraints here for data structure selection. Here, code provided an example with a map data structure with mixups of string. Regarding shell command, the os/exec package provides functionality that you are needing here (exec.Command). Run your code in Playground:

package main

import (
	"bufio"
	"fmt"
	"os"
	"os/exec"
	"strings"
)

type UserGroups map[string][]string

func main() {
	file, err := os.Open("/etc/passwd")
	if err != nil {
		panic(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)

	userGroups := make(UserGroups)

	for scanner.Scan() {
		fields := strings.Split(scanner.Text(), ":")

		username := fields[0]

		cmd := exec.Command("id", "-Gn", username)
		output, err := cmd.Output()
		if err != nil {
			panic(err)
		}

		groups := strings.Split(strings.TrimSpace(string(output)), " ")

		userGroups[username] = groups
	}

	for username, groups := range userGroups {
		fmt.Printf("%s: %s\n", username, strings.Join(groups, ", "))
	}
}

Playground output:

operator: operator
mail: mail
www-data: www-data
bin: bin
sys: sys
sync: users
nobody: nobody
root: root, wheel
daemon: daemon
Program exited.