Lua Cheat Sheet

Lua is a lightweight, embeddable scripting language widely used in game development, embedded systems, and configuration environments. This Lua cheatsheet is a structured, example-driven reference covering core syntax, tables, functions, metatables, and coroutine-based concurrency.

Basic Program

print("Hello, Lua")

Variables

a = 10
b = "text"
c = true

local x = 5

Data Types

number
string
boolean
table
function
userdata
thread
nil

type(10)
type("lua")

Strings

s = "Lua"
s:upper()
s:lower()
string.len(s)

name = "World"
print("Hello " .. name)
print(string.format("Hello %s", name))

Operators

a + b
a - b
a * b
a / b
a % b
a ^ b

a == b
a ~= b
a > b
a < b

a and b
a or b
not a

Control Flow

if / elseif / else

if x > 10 then
  print("large")
elseif x > 5 then
  print("medium")
else
  print("small")
end

while

while x > 0 do
  x = x - 1
end

repeat / until

repeat
  x = x - 1
until x == 0

for

for i = 1, 5 do
  print(i)
end

for i = 1, 10, 2 do
  print(i)
end

Functions

function add(a, b)
  return a + b
end

result = add(2, 3)

Anonymous Functions

square = function(x)
  return x * x
end

Multiple Return Values

function divide(a, b)
  return a / b, a % b
end

q, r = divide(10, 3)

Tables

t = {1, 2, 3}

person = {
  name = "A",
  age = 20
}

Table Access

t[1]
person.name
person["age"]

Table Iteration

for i, v in ipairs(t) do
  print(i, v)
end

for k, v in pairs(person) do
  print(k, v)
end

Table Functions

table.insert(t, 4)
table.remove(t, 1)
table.sort(t)

Tables as Objects

Counter = {
  value = 0
}

function Counter:increment()
  self.value = self.value + 1
end

Counter:increment()

Metatables

mt = {}

function mt.__add(a, b)
  return { a[1] + b[1] }
end

setmetatable({1}, mt) + {2}

__index Metamethod

proto = {
  greet = function(self)
    print("hello")
  end
}

obj = {}
setmetatable(obj, { __index = proto })
obj:greet()

Modules

-- math_utils.lua
local M = {}

function M.add(a, b)
  return a + b
end

return M

local math_utils = require("math_utils")
math_utils.add(2, 3)

Coroutines

co = coroutine.create(function()
  print("start")
  coroutine.yield()
  print("end")
end)

coroutine.resume(co)
coroutine.resume(co)

Coroutine Status

coroutine.status(co)

Error Handling

error("failed")

status, err = pcall(function()
  error("fail")
end)

File I/O

file = io.open("file.txt", "w")
file:write("text")
file:close()

file = io.open("file.txt", "r")
content = file:read("*a")
file:close()

Environment Variables

os.getenv("PATH")

Command Line Arguments

for i, v in ipairs(arg) do
  print(i, v)
end

Time & Date

os.time()
os.date("%Y-%m-%d")