Lua Quick Reference

Quick Links

• Basics
• Operators
• Conditionals
• Loops
• Functions
• Tables
• Files

Basics

Console Output & Comments

print("Hello, world!") -- This is a comment.

Variables

local a = "String type"
b = true -- global
c, d = 5, nil

print(type(c), type(d)) -- number    nil

Strings

a = "Double"
b = 'Single'
c = [[
multiline
string
]]

string.upper(a)   -- DOUBLE
string.lower(a)   -- double
string.reverse(b) -- elgniS
string.len(b)     -- 6
#b                -- 6
a .. b            -- DoubleSingle

Operators

Arithmetic

a, b = 10, 5

a + b -- 15
a - b -- 5
a * b -- 50
a / b -- 2
a ^ b -- 100000.0
a % b -- 0
-a    -- -10

Relational

a, b = 4, 6

a == b -- false
a ~= b -- true
a > b  -- false
a < b  -- true
a <= b -- false
a >= b -- true

Logical

a, b = true, false

a and b -- false
a or b  -- true
not b   -- true

Conditionals

if condition then
    statements()
elseif other_condition then
    statements()
else
    statements()
end

Loops

while loop

i = 0

while i < 10
do
    print(i)
    i = i + 1
end -- returns 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

for loop

for i = 0, 10, 1
do
    print(i)
end -- returns 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

repeat loop

i = 0;

repeat
    print(i)
    i = i + 1
until i > 10 -- returns 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

break statement

for i = 10, 0, -1
do
    print(i)
    if i == 5 then
        break
    end
end -- returns 10, 9, 8, 7, 6, 5

Functions

function average(num1, num2)
    return (num1 + num2) / 2
end

print(average(10, 20)) -- 15.0

Tables

fruits = {"Banana", "Orange"}
print(fruits[1]) -- Banana

-- Removing elements

fruits[3] = "Apple"
table.remove(fruits) -- Apple
print(fruits[3]) -- nil

table.remove(fruits, 1) -- Banana
print(fruits[1]) -- Orange
print(#fruits) -- 1

-- Inserting elements

table.insert(fruits, "Mango")
table.insert(fruits, 2, "Papaya")

print(fruits[2]) -- Papaya
print(#fruits) -- 3

table.concat(fruits, " and ") -- Orange and Papaya and Mango

table.sort(fruits)

for key, value in ipairs(fruits) do
    print(key, value)
end

--[[
1       Mango
2       Orange
3       Papaya
]]

Files

Implicit

-- Writing

file = io.open("test.txt", "w")
io.output(file)

io.write("This creates a file and writes this line at the top!")

io.close(file) -- true

-- Reading

file = io.open("test.txt", "r")
io.input(file)

print(io.read()) -- This creates a file and writes this line at the top!

io.close(file) -- true

-- Appending

file = io.open("test.txt", "a")
io.output(file)

io.write("Appending to the test file!")

io.close(file) -- true

Explicit

-- Writing

file = io.open("test.txt", "w")

file:write("This creates a file and writes this line at the top!")

file:close() -- true

-- Reading

file = io.open("test.txt", "r")

file:read() -- This creates a file and writes this line at the top!

file:close() -- true

-- Appending

file = io.open("test.txt", "a")

file:write("Appending to the test file!")

file:close() -- true