Add a new sudoer user with password.

add_sudoer_user.sh

#!/usr/bin/env bash

set -o errexit
set -o pipefail

add_user() {
	local username="$1"
	local password="$2"

	if id -u "${username}" &>/dev/null; then
		return
	fi
	useradd -m -U -G wheel -s /bin/bash "${username}"
	echo "${username}:${password}" | chpasswd
}

add_sudoers() {
	local username="$1"

	chmod u+w /etc/sudoers
	if [[ "$(grep -P "${username}\tALL=\(ALL\)\s+?ALL" "/etc/sudoers" 2>/dev/null)" != "" ]]; then
		return
	fi
	echo -e "${username}\tALL=(ALL)\tALL" >> "/etc/sudoers"
	chmod u-w /etc/sudoers
}

main() {
	local username="$1"
	local password="$2"

	add_user "${username}" "${password}"
	add_sudoers "${username}"
}

main "$@"