Operators & Expressions

Arithmetic operators

Op	Name	Example	Notes
+	addition	a + b
-	subtraction	a - b	also unary negation
*	multiplication	a * b
/	float division	a / b	always returns float
//	floor division	a // b	rounds toward -∞
%	modulo	a % b	a % b == a - (a // b) * b
^	exponentiation	a ^ b	always returns float
~	bitwise NOT	~a	unary, NOT negation

Division behavior

print(10 / 3)    -- 3.3333... (float)
print(10 // 3)   -- 3         (integer)
print(-10 // 3)  -- -4        (floor toward -∞)
print(10.0 // 3) -- 3.0       (float floor)

Modulo

print(10 % 3)    -- 1
print(-10 % 3)   -- 2  (result has sign of second operand)

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Bitwise operators (integers only)

Op	Name	Example
&	AND	a & b
|	OR	a | b
~	XOR	a ~ b
>>	right shift	a >> n
<<	left shift	a << n
~	NOT (unary)	~a

print(0xff & 0x0f)   -- 15 (0x0f)
print(0x01 << 4)     -- 16
print(0xff >> 4)     -- 15
print(~0)             -- -1 (all bits set)

[!tip] Shift amounts can be negative x << -2 is equivalent to x >> 2.

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Relational operators

Op	Meaning
==	equal
~=	not equal
<	less than
>	greater than
<=	less or equal
>=	greater or equal

Rules

• Same type → compare values (integers and floats compare by value: 1 == 1.0 is true)
• Different types → always false (except integer/float coercion)
• Tables, userdata, threads → compared by reference (identity, not structure)
• nil only equals nil

print(1 == 1.0)       -- true (numeric comparison)
print("1" == 1)       -- false (different types)
print({} == {})       -- false (different tables)
local t = {}
print(t == t)         -- true (same reference)

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Logical operators

Op	Meaning	Behavior
and	logical AND	Returns first falsy operand, or last operand
or	logical OR	Returns first truthy operand, or last operand
not	logical NOT	Returns true or false

-- Short-circuit evaluation
print(nil and "hi")    -- nil
print(false and "hi")  -- false
print("a" and "hi")    -- "hi"

print(nil or "hi")     -- "hi"
print(false or "hi")   -- "hi"
print("a" or "hi")     -- "a"

-- Idioms
local x = v or default     -- default if v is nil/false
local max = (a > b) and a or b  -- ternary-ish (caution: fails if a is falsy)

[!warning] Ternary idiom trap (cond) and a or b fails if a is falsy. Use if/else for safety.

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Concatenation

local s = "hello" .. " " .. "world"  -- "hello world"
local n = "value: " .. 42            -- error in 5.4! Use tostring()
local ok = "value: " .. tostring(42) -- "value: 42"

[!important] No implicit number→string in 5.4 "x" .. 1 raises an error. Always tostring().

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Length operator

#s          -- string length (bytes)
#t          -- table length (border of sequence)

For tables, #t returns the border: the index i such that t[i] is not nil and t[i+1] is nil.

print(#"hello")      -- 5
print(#{10, 20, 30}) -- 3
print(#{1, nil, 3})  -- 1 or 3 (undefined!)

[!warning] Non-sequences # on tables with gaps (nil holes) is undefined. Use ipairs or explicit counting instead.

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Operator precedence

Higher = tighter binding:

Priority	Op	Associativity
1 (highest)	^	right
2	unary: not # - ~	right
3	* / // %	left
4	+ -	left
5	..	right
6	<< >>	left
7	&	left
8	~ (binary XOR)	left
9	|	left
10	< > <= >= ~= ==	none
11	and	left
12 (lowest)	or	left

-- Precedence examples
a + b * c         -- a + (b * c)
a ^ b ^ c         -- a ^ (b ^ c)  -- right assoc
a .. b .. c       -- a .. (b .. c) -- right assoc
not a == b        -- (not a) == b
a and b or c      -- (a and b) or c

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Expressions

Parenthesized

(a + b) * c

Function calls

f()
f(a, b)
t:m()

Varargs expression

...     -- expands to all variable arguments

Table constructors

{1, 2, 3}
{x = 1, y = 2}
{[f(1)] = g; "x", "y"}

See Tables for details.