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Catalog / Lua Cheatsheet

Lua Cheatsheet

A comprehensive cheat sheet for the Lua scripting language, covering syntax, data structures, control flow, functions, metatables, and common APIs.

Lua Basics

Syntax and Comments

Single-line comment:

-- This is a comment

Multi-line comment:

--[[ This is a multi-line comment ]]

Variables:

local myVariable = 10

Assignment:

x = 1; y = 'hello'

Multiple assignment:

a, b = 1, 2

Data Types

Nil:

nil (absence of a value)

Boolean:

true, false

Number:

42, 3.14159

String:

'hello', "world"

Table:

Associative array (object)

Function:

First-class citizen

Operators

Arithmetic: +, -, *, /, %, ^ (exponentiation), - (unary minus)

Relational: ==, ~=, <, >, <=, >=

Logical: and, or, not

String Concatenation: ..

Length Operator: # (length of a table or string)

Control Flow

Conditionals 

if condition then
  -- code
elseif condition then
  -- code
else
  -- code
end

Example:

 
if x > 10 then
  print("x is greater than 10")
elseif x < 10 then
  print("x is less than 10")
else
  print("x is equal to 10")
end

Loops

While Loop:

 
while condition do
  -- code
end

For Loop (numeric):

 
for i = start, end, step do
  -- code
end

For Loop (generic):

 
for key, value in pairs(table) do
  -- code
end

Repeat-Until Loop:

 
repeat
  -- code
until condition

Loop Control

Break:

Exits the current loop.

Return:

Exits the current function.

Tables and Functions

Tables

Table Creation:

 
table = {}

Adding Key-Value Pairs:

 
table["key"] = "value"
table.key = "value"  -- Equivalent when key is a valid identifier

Accessing Values:

 
value = table["key"]
value = table.key

Arrays (Tables with Numeric Indices):

 
array = {"a", "b", "c"}
print(array[1])  -- "a" (Lua is 1-indexed)

Functions

Function Definition:

 
function functionName(arg1, arg2)
  -- code
  return value
end

Calling a Function:

 
result = functionName(value1, value2)

Anonymous Functions:

 
myFunc = function(x)
  return x * 2
end

Variable Arguments:

 
function varArgFunc(a, ...)
  local args = { ... }
  for i, v in ipairs(args) do
    print(i, v)
  end
end

Scope

Global:

Accessible everywhere.

Local:

Accessible only within its scope (e.g., function or block).

Metatables and Object Orientation

Metatables

Setting a Metatable:

 
mt = {}
setmetatable(table, mt)

Common Metamethods:
  • __index: Table indexing fallback.
  • __newindex: Table assignment fallback.
  • __add, __sub, __mul, __div: Arithmetic operators.
  • __tostring: String conversion.

Example:

 
mt.__index = function(table, key)
  return "Default Value"
end

Object Orientation

Creating a Class:

 
MyClass = {}
MyClass.__index = MyClass

Constructor:

 
function MyClass:new(value)
  local self = setmetatable({}, MyClass)
  self.value = value
  return self
end

Methods:

 
function MyClass:getValue()
  return self.value
end

Usage:

 
local instance = MyClass:new(10)
print(instance:getValue())

Common APIs

String Library

string.len(s): Returns the length of the string s.

string.sub(s, i, j): Extracts a substring from s starting at index i and ending at index j.

string.find(s, pattern, init, plain): Searches for the first occurrence of pattern in s. init is an optional starting index, and plain is a boolean to disable pattern matching.

string.gsub(s, pattern, repl, n): Replaces occurrences of pattern in s with repl. n is an optional maximum number of replacements.

string.format(formatstring, …): Returns a formatted string using the given format string and arguments.

string.upper(s), string.lower(s): Converts the string s to uppercase or lowercase, respectively.

Table Library

table.insert(t, pos, value): Inserts value into table t at position pos. If pos is omitted, it defaults to #t + 1 (appends to the end).

table.remove(t, pos): Removes the element at position pos from table t. Returns the value of the removed element.

table.sort(t, comp): Sorts the elements of table t in place, using the optional comparison function comp.

table.concat(t, sep, i, j): Concatenates the strings in table t from index i to j, with sep as a separator string.

Math Library

math.random(m, n): Returns a pseudo-random number. If called without arguments, returns a float between 0 and 1. If called with two integer arguments m and n, returns an integer between m and n.

math.abs(x): Returns the absolute value of x.

math.floor(x), math.ceil(x): Returns the largest integer less than or equal to x, or the smallest integer greater than or equal to x, respectively.

math.sqrt(x): Returns the square root of x.

math.sin(x), math.cos(x), math.tan(x): Trigonometric functions (x in radians).

math.pi: The value of pi.
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