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Lua Cheatsheet

A concise reference for Lua syntax, data types, control structures, and standard library functions. Perfect for quick lookup and reminding yourself of the essentials.

Basics & Syntax

Basic Syntax

Comments

-- Single-line comment
--[[ ... --]] Multi-line comment

Variables

local - Scope limited to the block
variable_name = value - Global scope if not declared local

Assignment

= Assignment operator

Chaining Assignment

a, b = 10, 20 Assigns 10 to a and 20 to b.

Statements

Statements do not need to end with a semicolon (;)

Case Sensitivity

Lua is case sensitive

Data Types

  • nil: Represents the absence of a value.
  • boolean: true or false.
  • number: Represents real (double-precision floating-point) numbers.
  • string: Immutable sequence of characters.
  • table: Associative array (hash table). The primary data structure in Lua.
  • function: First-class functions.
  • userdata: Raw memory blocks, used to represent new types created in C.

Operators

Arithmetic Operators

+, -, *, /, ^ (exponentiation), % (modulo)

Relational Operators

== (equal), ~= (not equal), <, >, <=, >=

Logical Operators

and, or, not

Concatenation Operator

.. (string concatenation)

Length Operator

# (length of a string or table)

Control Structures

Conditional Statements

if condition then ... end
if condition then ... else ... end
if condition then ... elseif condition then ... else ... end

Example:

if age >= 18 then
  print("Adult")
else
  print("Minor")
end

Looping Statements

while condition do ... end
repeat ... until condition
for i = start, end, step do ... end
for key, value in pairs(table) do ... end

Example (while loop):

i = 1
while i <= 5 do
  print(i)
  i = i + 1
end

Example (for loop):

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

Example (foreach loop):

my_table = {"a", "b", "c"}
for index, value in ipairs(my_table) do
  print(index, value)
end

Break and Return

break

Exits the innermost loop.

return

Exits the function.

Tables

Table Basics

Tables are the primary data structure in Lua. They are associative arrays that can be indexed with any value (except nil).

Table Creation and Access

Creating a Table

my_table = {} (empty table)
my_table = {key1 = "value1", key2 = "value2"}
my_table = {"value1", "value2", "value3"} (array-like table)

Accessing Elements

my_table.key1 or my_table["key1"] (using string keys)
my_table[1] (using numerical indices - 1-based)

Adding/Modifying Elements

my_table.new_key = "new_value"
my_table["existing_key"] = "updated_value"

Removing Elements

my_table.key = nil

Table Functions

  • table.insert(table, [pos,] value): Inserts a new element at a given position.
  • table.remove(table, [pos]): Removes an element at a given position.
  • table.sort(table, [comp]): Sorts the table elements.
  • table.concat(table, [sep, i, j]): Concatenates elements of a table into a string.

Example (insert):

table.insert(my_table, 1, "first")

Example (remove):

table.remove(my_table, 2)

Functions

Function Definition

function function_name(arg1, arg2, ...) ... end
local function function_name(arg1, arg2, ...) ... end (local function)

Example:

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

Function Calls

Calling a Function

function_name(arg1, arg2, ...)

Calling a Method

object:method_name(arg1, arg2, ...) (equivalent to object.method_name(object, arg1, arg2, ...))

Returning Values

Functions can return multiple values: return value1, value2

Variable Arguments

Use ... to accept a variable number of arguments.
Arguments are accessed via the arg table (deprecated in Lua 5.2, use ... directly).
Use table.pack(...) to pack the arguments into a table, which also stores the number of arguments.

Example:

function sum(...)
  local total = 0
  local args = {...}
  for i, v in ipairs(args) do
    total = total + v
  end
  return total
end

print(sum(1, 2, 3, 4)) -- Output: 10
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