GroupService

local Players = game:GetService("Players")
local GroupService = game:GetService("GroupService")

local GROUP_ID = 57

-- creates a table of all of the allies of a given group
local allies = {}

local pages = GroupService:GetAlliesAsync(GROUP_ID)

while true do
	for _, group in pairs(pages:GetCurrentPage()) do
		table.insert(allies, group)
	end
	if pages.IsFinished then
		break
	end
	pages:AdvanceToNextPageAsync()
end

function onPlayerAdded(player)
	for _, group in pairs(allies) do
		if player:IsInGroup(group.Id) then
			print("Player is an ally!")
			break
		end
	end
end

Players.PlayerAdded:Connect(onPlayerAdded)
-- handle players who joined while the allies list was still loading
for _, player in pairs(Players:GetPlayers()) do
	onPlayerAdded(player)
end

local GroupService = game:GetService("GroupService")
local Players = game:GetService("Players")

-- define group id here
local GROUP_ID = 271454

-- utility function for dealing with pages
local function pagesToArray(pages)
	local array = {}
	while true do
		for _, v in ipairs(pages:GetCurrentPage()) do
			table.insert(array, v)
		end
		if pages.IsFinished then
			break
		end
		pages:AdvanceToNextPageAsync()
	end
	return array
end

-- get lists of allies and enemies
local alliesPages = GroupService:GetAlliesAsync(GROUP_ID)
local enemiesPages = GroupService:GetEnemiesAsync(GROUP_ID)

-- convert to array
local allies = pagesToArray(alliesPages)
local enemies = pagesToArray(enemiesPages)

local function playerAdded(player)
	-- check to see if the player is in the group
	if player:IsInGroup(GROUP_ID) then
		print(player.Name .. " is a member!")
	else
		local isAlly, isEnemy = false, false

		-- check to see if the player is in any ally groups
		for _, groupInfo in ipairs(allies) do
			local groupId = groupInfo.Id
			if player:IsInGroup(groupId) then
				isAlly = true
				break
			end
		end

		-- check to see if the player is in any enemy groups
		for _, groupInfo in ipairs(enemies) do
			local groupId = groupInfo.Id
			if player:IsInGroup(groupId) then
				isEnemy = true
				break
			end
		end

		if isAlly and not isEnemy then
			print(player.Name .. " is an ally!")
		elseif isEnemy and not isAlly then
			print(player.Name .. " is an enemy!")
		elseif isEnemy and isAlly then
			print(player.Name .. " is both an ally and an enemy!")
		else
			print(player.Name .. " is neither an ally or an enemy!")
		end
	end
end

-- listen for new players being added
Players.PlayerAdded:Connect(playerAdded)

-- handle players already in game
for _, player in ipairs(Players:GetPlayers()) do
	playerAdded(player)
end

local Players = game:GetService("Players")
local GroupService = game:GetService("GroupService")

local GROUP_ID = 57

-- creates a list of all of the enemies of a given group
local enemies = {}

local pages = GroupService:GetEnemiesAsync(GROUP_ID)

while true do
	for _, group in pairs(pages:GetCurrentPage()) do
		table.insert(enemies, group)
	end
	if pages.IsFinished then
		break
	end
	pages:AdvanceToNextPageAsync()
end

function onPlayerAdded(player)
	for _, enemyGroup in pairs(enemies) do
		if player:IsInGroup(enemyGroup.Id) then
			print("Player is an enemy!")
			break
		end
	end
end

Players.PlayerAdded:Connect(onPlayerAdded)
-- handle players who joined while the enemies list was still loading
for _, player in pairs(Players:GetPlayers()) do
	onPlayerAdded(player)
end

local GroupService = game:GetService("GroupService")
local Players = game:GetService("Players")

-- define group id here
local GROUP_ID = 271454

-- utility function for dealing with pages
local function pagesToArray(pages)
	local array = {}
	while true do
		for _, v in ipairs(pages:GetCurrentPage()) do
			table.insert(array, v)
		end
		if pages.IsFinished then
			break
		end
		pages:AdvanceToNextPageAsync()
	end
	return array
end

-- get lists of allies and enemies
local alliesPages = GroupService:GetAlliesAsync(GROUP_ID)
local enemiesPages = GroupService:GetEnemiesAsync(GROUP_ID)

-- convert to array
local allies = pagesToArray(alliesPages)
local enemies = pagesToArray(enemiesPages)

local function playerAdded(player)
	-- check to see if the player is in the group
	if player:IsInGroup(GROUP_ID) then
		print(player.Name .. " is a member!")
	else
		local isAlly, isEnemy = false, false

		-- check to see if the player is in any ally groups
		for _, groupInfo in ipairs(allies) do
			local groupId = groupInfo.Id
			if player:IsInGroup(groupId) then
				isAlly = true
				break
			end
		end

		-- check to see if the player is in any enemy groups
		for _, groupInfo in ipairs(enemies) do
			local groupId = groupInfo.Id
			if player:IsInGroup(groupId) then
				isEnemy = true
				break
			end
		end

		if isAlly and not isEnemy then
			print(player.Name .. " is an ally!")
		elseif isEnemy and not isAlly then
			print(player.Name .. " is an enemy!")
		elseif isEnemy and isAlly then
			print(player.Name .. " is both an ally and an enemy!")
		else
			print(player.Name .. " is neither an ally or an enemy!")
		end
	end
end

-- listen for new players being added
Players.PlayerAdded:Connect(playerAdded)

-- handle players already in game
for _, player in ipairs(Players:GetPlayers()) do
	playerAdded(player)
end

local GroupService = game:GetService("GroupService")

local GROUP_ID = 377251

local group = GroupService:GetGroupInfoAsync(GROUP_ID)

print(group.Name .. " has the following roles:")
for _, role in ipairs(group.Roles) do
	print("Rank " .. role.Rank .. ": " .. role.Name)
end

local GroupService = game:GetService("GroupService")

local function getEmblemAsync(groupId)
	local groupInfo = GroupService:GetGroupInfoAsync(groupId)
	return groupInfo.EmblemUrl
end

local part = Instance.new("Part")
part.Anchored = true
part.CanCollide = false
part.Size = Vector3.new(5, 5, 1)
part.Position = Vector3.new(0, 5, 0)

local decal = Instance.new("Decal")
decal.Parent = part
part.Parent = workspace

decal.Texture = getEmblemAsync(377251)

local GroupService = game:GetService("GroupService")
local Players = game:GetService("Players")

local function playerAdded(player)
	-- load a list of info on all groups the player is a member of
	local groups = GroupService:GetGroupsAsync(player.UserId)

	for _, groupInfo in pairs(groups) do
		for key, value in pairs(groupInfo) do
			print(key .. ": " .. tostring(value))
		end

		print("--")
	end
end

Players.PlayerAdded:Connect(playerAdded)

-- go through existing players
for _, player in pairs(Players:GetPlayers()) do
	playerAdded(player)
end