Lua Cheat Sheet

Learn Lua from the basics →

Variables & Types

local name = "Ada": Local variable (always prefer local)
local a, b = 1, 2: Multiple assignment
type(x): nil, boolean, number, string, table, function, thread, userdata
tonumber("42") / tostring(42): Convert (tonumber returns nil on failure)
math.type(3) / math.type(3.0): "integer" / "float" (Lua 5.3+)
x = x or "default": Default value (only nil and false are falsy)

Strings

"Hello, " .. name: Concatenation
#s: Length in bytes
string.format("%s is %d", name, age): Formatted string
s:upper() / s:lower() / s:rep(3): Method call syntax on strings
s:sub(2, 4): Substring (1-based, inclusive)
[[multi-line string]]: Long string, no escapes processed

Control Flow

if x > 0 then ... elseif x < 0 then ... else ... end: Conditional
for i = 1, 10 do ... end: Numeric loop (inclusive); for i = 10, 1, -1 counts down
for i, v in ipairs(list) do ... end: Loop over an array in order
for k, v in pairs(t) do ... end: Loop over all keys (no guaranteed order)
while cond do ... end / repeat ... until cond: Condition loops
break / goto continue: Exit a loop / jump to a ::continue:: label

Tables

local list = {10, 20, 30}: Array — indexes start at 1
local user = {name = "Ada", age = 36}: Record / dictionary
user.name / user["name"]: Field access
table.insert(list, 40) / list[#list + 1] = 40: Append
table.remove(list, 1): Remove by position
table.concat(list, ", ") / table.sort(list): Join / sort in place

Functions

local function add(a, b) return a + b end: Local function
local sq = function(x) return x * x end: Anonymous function
return a, b: Multiple return values
function f(...) local n = select("#", ...) end: Variadic function
obj:method(x): Same as obj.method(obj, x)

Metatables & OOP

setmetatable(t, mt): Attach a metatable
mt.__index = Class: Fall back to Class for missing keys (methods)
mt.__add / __eq / __lt / __tostring / __call: Operator overloading
function Class.new(x) return setmetatable({x = x}, Class) end: Constructor

Errors & Modules

error("message"): Raise an error
local ok, err = pcall(f, arg): Call in protected mode
assert(x, "message"): Error if x is nil or false
local M = {} ... return M: Module file pattern
local utils = require("utils"): Load a module (cached after first load)

Coroutines

local co = coroutine.create(f): Create a coroutine
coroutine.resume(co, ...): Start or continue it
coroutine.yield(value): Pause and hand a value back
coroutine.wrap(f): Coroutine as a callable generator