Lua cheat sheet

local Account = {}
Account.__index = Account
 
function Account.new(owner, balance)
  local self = setmetatable({}, Account)
  self.owner = owner
  self.balance = balance or 0
  return self
end
 
function Account:deposit(amount)
  if amount <= 0 then
    error("deposit must be positive", 2)
  end
  self.balance = self.balance + amount
  return self
end
 
function Account:withdraw(amount)
  if amount > self.balance then
    return nil, "insufficient funds"
  end
  self.balance = self.balance - amount
  return self.balance
end
 
Account.__tostring = function(a)
  return string.format("%s: %.2f", a.owner, a.balance)
end
 
Account.__lt = function(a, b) return a.balance < b.balance end
 
-- A subclass: look up missing methods on Account.
local Savings = setmetatable({}, { __index = Account })
Savings.__index = Savings
Savings.__tostring = Account.__tostring
Savings.__lt = Account.__lt
 
function Savings.new(owner, balance, rate)
  local self = Account.new(owner, balance)
  self.rate = rate
  return setmetatable(self, Savings)
end
 
function Savings:add_interest()
  return self:deposit(self.balance * self.rate)
end
 
local ada = Account.new("Ada", 100):deposit(50)
local alan = Savings.new("Alan", 200, 0.05):add_interest()
 
print(ada)                         --> Ada: 150.00
print(alan)                        --> Alan: 210.00
print(ada < alan)                  --> true
print(ada:withdraw(500))           --> nil  insufficient funds
print(pcall(ada.deposit, ada, -5)) --> false  deposit must be positive

-- greeter.lua
local M = {}
 
local default_name = "world" -- private: not in M
 
function M.hello(name)
  return "Hello, " .. (name or default_name)
end
 
function M.shout(name)
  return M.hello(name):upper() .. "!"
end
 
return M

-- main.lua, in the same folder
local greeter = require("greeter")
 
print(greeter.hello())      --> Hello, world
print(greeter.shout("Ada")) --> HELLO, ADA!

local log = [[
2026-09-26 12:01:07 INFO  user=ada action=login
2026-09-26 12:03:44 ERROR user=alan action=upload size=12MB
2026-09-26 12:04:02 INFO  user=ada action=logout
]]
 
local counts = {}
for date, time, level, rest in log:gmatch("(%d+%-%d+%-%d+) (%d+:%d+:%d+) (%u+)%s+([^\n]*)") do
  counts[level] = (counts[level] or 0) + 1
 
  -- Pull key=value pairs out of the rest of the line into a table.
  local fields = {}
  for key, value in rest:gmatch("(%w+)=(%w+)") do
    fields[key] = value
  end
 
  if level == "ERROR" then
    print(time, fields.user, fields.action) --> 12:03:44  alan  upload
  end
end
 
print(counts.INFO, counts.ERROR) --> 2  1
 
-- Escape the magic characters ( ) . % + - * ? [ ] ^ $ with %.
local price = "Total: $4.50"
print(price:match("%$(%d+%.%d+)")) --> 4.50
 
-- Or search for plain text with the fourth argument to find.
print(price:find("$4.", 1, true)) --> 8  10

-- A generator: yields values one at a time, keeps its place between calls.
local function range(from, to, step)
  return coroutine.wrap(function()
    for i = from, to, step or 1 do
      coroutine.yield(i)
    end
  end)
end
 
for n in range(10, 30, 10) do
  print(n) --> 10, 20, 30
end
 
-- A pipeline: each stage pulls from the one before it.
local function lines(text)
  return coroutine.wrap(function()
    for line in text:gmatch("[^\n]+") do
      coroutine.yield(line)
    end
  end)
end
 
local function non_blank(source)
  return coroutine.wrap(function()
    for line in source do
      if line:find("%S") then
        coroutine.yield(line)
      end
    end
  end)
end
 
for line in non_blank(lines("alpha\n   \nbeta\n")) do
  print(line) --> alpha, beta
end
 
-- Passing values both ways with resume and yield.
local acc = coroutine.create(function(first)
  local total = first
  while true do
    local n = coroutine.yield(total)
    total = total + n
  end
end)
 
print(coroutine.resume(acc, 5))  --> true  5
print(coroutine.resume(acc, 10)) --> true  15
print(coroutine.status(acc))     --> suspended

-- Lua 5.5: from here on, every name must be declared.
-- Existing globals such as print and string can be read but not reassigned.
global<const> *
 
-- Globals this file is allowed to set.
global config, VERSION
 
VERSION = "1.2.0"
config = { debug = false }
 
local function load_settings()
  cofnig = { debug = true } -- typo: compile error, not a silent new global
end

-- A Script in ServerScriptService. Luau, not Lua 5.5.
local Players = game:GetService("Players")
 
local STARTING_COINS = 100
 
Players.PlayerAdded:Connect(function(player: Player)
	local stats = Instance.new("Folder")
	stats.Name = "leaderstats"
	stats.Parent = player
 
	local coins = Instance.new("IntValue")
	coins.Name = "Coins"
	coins.Value = STARTING_COINS
	coins.Parent = stats
 
	print(`{player.Name} joined with {coins.Value} coins`)
end)
 
while true do
	task.wait(60)
	for _, player in Players:GetPlayers() do
		local stats = player:FindFirstChild("leaderstats")
		local coins = stats and stats:FindFirstChild("Coins")
		if coins then
			coins.Value += 10
		end
	end
end

-- ~/.config/nvim/init.lua
vim.g.mapleader = " "
 
vim.opt.number = true
vim.opt.expandtab = true
vim.opt.shiftwidth = 2
 
vim.keymap.set("n", "<leader>w", "<cmd>write<cr>", { desc = "Save the file" })
 
vim.api.nvim_create_autocmd("TextYankPost", {
  desc = "Flash the text you just yanked",
  callback = function()
    vim.hl.on_yank()
  end,
})

-- main.lua for LÖVE: run the folder with `love .`
local player = { x = 100, y = 100, speed = 200 }
 
function love.load()
  love.window.setTitle("Move the square")
end
 
function love.update(dt)
  -- dt is the seconds since the last frame, so speed is per second.
  if love.keyboard.isDown("right") then player.x = player.x + player.speed * dt end
  if love.keyboard.isDown("left") then player.x = player.x - player.speed * dt end
end
 
function love.draw()
  love.graphics.rectangle("fill", player.x, player.y, 32, 32)
end