An operator is a symbol for performing an operation or conditional evaluation.

## Logical

Logical operators return values depending on the boolean values of the given arguments. If an argument isn't false or nil, then the operator evaluates it as true. Unlike many other languages, Luau considers both zero and the empty string as true. The following table summarizes how logical operators behave in conditionals.

Operator | Descriptions |
---|---|

and | Evaluates as true only if both conditions are true |

or | Evaluates as true if either condition is true |

not | Evaluates as the opposite of the condition |

### and

The binary operator and returns one of the two arguments. If the first argument evaluates to true, then it returns the second argument. Otherwise, it returns the first argument.

print(4 and 5) -- 5print(nil and 12) -- nilprint(false and 12) -- falseprint(false and true) -- falseprint(false and false) -- falseprint(true and false) -- falseprint(true and true) -- true

You can use and to test multiple conditions in control structures such as if statements and while loops. For example, the following if—then statement tests that two conditions are both true:

local pasta = truelocal tomatoSauce = trueif pasta == true and tomatoSauce == true thenprint("We have spaghetti dinner")elseprint("Something is missing...")end-- Output: We have spaghetti dinner

### or

The binary operator or returns one of the two arguments. If the first argument evaluates to true, then it returns the first argument. Otherwise, it returns the second argument.

local y = x or 1print(y) -- 1 because x doesn't exist and is therefore nillocal d = falselocal e = d or 1print(e) -- 1 because d is falseprint(4 or 5) -- 4print(nil or 12) -- 12print(false or 12) -- 12print(false or true) -- trueprint(false or false) -- falseprint(true or false) -- trueprint(true or true) -- true

You can use or to perform complex logical tests in control structures. For example, the following if—then statement tests whether two conditions are true or a third condition is true:

local pasta = falselocal tomatoSauce = truelocal garlicBread = trueif (pasta == true and tomatoSauce == true) or garlicBread == true thenprint("We have either spaghetti dinner OR garlic bread")elseprint("Something is missing...")end-- Output: We have either spaghetti dinner OR garlic bread

### not

The unary operator not returns the opposite boolean value of the argument. If the argument is false or nil, then it returns true. Otherwise, it returns false.

print(not true) -- falseprint(not false) -- trueprint(not nil) -- trueprint(not "text") -- falseprint(not 0) -- false

You can use the not operator to trigger a conditional or loop if a variable is false or nil.

local nilVariable -- Variable is declared but has no value, so it's nillocal falseVariable = false -- Variable is declared with value of falseif not nilVariable thenprint(nilVariable) -- Outputs "nil" because nil isn't trueendif not falseVariable thenprint(falseVariable) -- Outputs "false" because false isn't trueend

You can also use the not operator to test for the opposite of a entire multi-condition statement. In the following code sample, the if—then conditional tests that it's neither true that three is greater than four nor is it true that five is greater than four.

local three = 3local four = 4local five = 5if not (three > four or five < four) thenprint("Three is less than 4 and five is greater than 4.")end-- Output: Three is less than 4 and five is greater than 4.

## Relational

Relational operators compare two parameters and return a boolean: true or false.

Operator | Description | Example | Associated metamethod |
---|---|---|---|

== | Equal to | 3 == 5 → false |
__eq |

~= | Not equal to | 3 ~= 5 → true | |

> | Greater than | 3 > 5 → false | |

< | Less than | 3 < 5 → true |
__lt |

>= | Greater than or equal to | 3 >= 5 → false | |

<= | Less than or equal to | 3 <= 5 → true |
__le |

## Arithmetic

Lua supports the usual binary operators along with exponentiation, modulus, and unary negation.

Operator | Description | Example | Associated metamethod |
---|---|---|---|

+ | Addition | 1 + 1 = 2 | __add |

- | Subtraction | 1 - 1 = 0 | __sub |

* | Multiplication | 5 * 5 = 25 | __mul |

/ | Division | 10 / 5 = 2 | __div |

^ | Exponentiation | 2 ^ 4 = 16 | __pow |

% | Modulus | 13 % 7 = 6 | __mod |

- | Unary negation | -2 = 0 - 2 | __unm |

## Compound Assignment

You can use compound assignment operators to set a variable equal to the result of an operation where the first parameter is the variable's current value.

The operation in a compound assignment occurs once. For example, if an expression generates a random index in a table, Luau uses the same index for both the operation and the assignment.

In the following examples, suppose local x = 3.

Operator | Operation | Example | New Value of x |
---|---|---|---|

+= | Addition | x += 2 | 5 |

-= | Subtraction | x -= 2 | 1 |

*= | Multiplication | x *= 2 | 6 |

/= | Division | x /= 2 | 1.5 |

%= | Modulus | x %= 2 | 1 |

^= | Exponentiation | x ^= 2 | 9 |

..= | Concatenation | x ..= " World!" | "2 World!" |

## Miscellaneous

Miscellaneous operators include concatenation and length.

Operator | Description | Example | Associated metamethod |
---|---|---|---|

.. | Concatenates two strings | print("Hello " .. "World!") | __concat |

# | Length of table | If tableVar = {1, 2, 3}, then #tableVar == 3. | __len |