If you are just starting to program with Lua, welcome. This is part 2 of Programming Lua series.

In this short tutorial, I am going to demonstrate how to create variables to store data in Lua.

Launch Lua REPL

Lua ships with a program called REPL (REPL stands for Read Evaluate Print Loop) where you can try out Lua code. So, let’s launch the Lua REPL by running the lua command. When you invoke the Lua REPL, you should see something like this

✗ lua
Lua 5.3.5  Copyright (C) 1994-2018 Lua.org, PUC-Rio
>

Creating a variable

Every variable in Lua is required to wear an ID badge that identifies it. We give the variable this ID badge when we create the variable.

Let’s create a variable to store our name. We are going to give this variable the identifier name. So, let’s just type in name into the REPL.

> name
nil

Boom. We created a variable!!!

Creating multiple variables together

You can create multiple variables at the same time. Just add a comma in between each variable identifier that you want to create.

Let’s say that I wanted to store my age along with my name, I can create two variables to store that data and give them identifiers name and age.

> name, age
nil	nil

Assigning value to a variable

You can assign a value to the variable by using the = operator. We also call this the assignment operator. I am going to assign my name to the name variable.

> name = "Adhithya"

Quick Side Note: If you create a variable and do not assign anything, Lua REPL will assign nil as the value to that variable. This is what happened when we create the variable name originally and that’s why Lua REPL printed out nil in response.

> name
nil

Let’s understand nil a little bit better.

Nil value

nil is a special value in Lua that indicates nothing. If you assign nil to some variable, it means that you are telling Lua that you are storing nothing in that variable.

Assigning values to multiple variables

The assignment operator can be used to assign values to multiple variables at the same time.

> name, age = "Adhithya", 30

Change value stored in the variable

Lua allows us to change the contents stored inside variables anytime. We in the computer science biz like to that property mutability of variables. Let’s say that I accidentally misspell my name (which happens more often than I care to admit). Lua allows me to fix it by using the = or assignment operator again and providing the correct spelling as the value.

> name = "Aditya" -- wrong spelling
> name = "Adhithya" -- correct spelling

Type of contents stored in variables

Lue doesn’t require you to specify the type of the content to be stored in variable ahead of time. Lua automatically figures out the type of the content you have stored in the variable. If you run the type command, Lua will tell you the type it figured out.

> type(name)
string

Since types of the content stored in variables are not set in stone in Lua, you can change the type of the content stored in the variable after the variable was created. For example: You can assign a number to the variable name and Lua will not blink an eye. If you came from a statically typed language like C++, your head might be exploding right now haha.

> name = 2
> name
2

But, please don’t do what I did above. It makes it impossible to read the code.

Allowed variable identifiers

Lua requires the variable identifiers to meet certain rules

1. Variable identifiers should start with a letter or underscore.
2. Variable identifiers cannot contain spaces.
3. Lua has a set of reserved keywords. Lua doesn’t allow those reserved keywords to be used as a variable identifier. You can find a list of all the reserved keywords at https://www.lua.org/manual/5.1/manual.html

Here are some variable identifiers that are allowed

age = 5
start_counter = 10
_name = "Adhithya"
_1stChoice = true

Here are some variable identifiers that are not allowed

1stChoice = true 
-- Problem: A variable identifier cannot start with a letter
and = 2
-- Problem: and is a reserved keyword. It cannot be used as a variable identifer