Lua Cheetsheet

Comments

-- Single line comment
 
--[[
A multi-line comment
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Types

type(nil)               --> nil
type(true)              --> boolean
type(10.4*3)            --> number
type("Hello World")     --> string
type(is.stdin)          --> userdata (C FFI)
type(print)             --> function
type({})                --> table

Booleans

-- `false` and `nil` evals are falsy in lua.
-- all other values are truthy
 
e1 and e2 --> e1 if e1 is falsy else e2
e1 or e2 --> e1 if e1 is truthy else e2
not e --> true if e1 is falsy else false
-- Both `and` and `or` are short-circuit
 
x = x or v -- equivalent to
if not x then x = v end
a and b or c --> equivalent to a ? b : c in other language

Numbers

Numerals

type(3) --> number
type(3.0) --> number
math.type(3) --> integer
math.type(3.0) --> float
0xff    --> 255
0x0.2   --> 0.125
0x1p-1  --> 0.5     same as 1 * (2 ^ -1)
0xa.bp2 --> 42.75   same as a.b * (2 ^ 2)

Arithmetic Operators

e1 + e2  --> math.type is integer if both e1 and e2 are integers else float
e1 - e2 
e1 * e2
e1 / e2  --> always type float
e1 // e2 --> floor divition. always rounds the quotient towards minus infinity
         -- Type is integer if both e1 and e2 are integers else float
e1 % e2  --> modulo operator. equiv to `e1 - ((e1 // e2) * e2)`
e1 ^ e2  --> exponential. always type float

Relational Operators

e1 < e2
e1 > e2
e1 <= e2
e1 >= e2
e1 == e2
e1 ~= e2

Strings

-- string in lua is immutable
a = "one string"
b = string.gsub(a, "one", "another") --> "another string"
#a --> 10. length of string
#"hello" --> 5
"Hello " .. "World"  --> "Hello World" string concatenation
"result is " .. 3    --> "result is 3"