This first edition was written for Lua 5.0. While still largely relevant for later versions, there are some differences.
The fourth edition targets Lua 5.3 and is available at Amazon and other bookstores.
By buying the book, you also help to support the Lua project.

Part I. The Language Chapter 1. Getting Started

1 – Getting Started

To keep with the tradition, our first program in Lua just prints "Hello World":

    print("Hello World")

If you are using the stand-alone Lua interpreter, all you have to do to run your first program is to call the interpreter (usually named lua) with the name of the text file that contains your program. For instance, if you write the above program in a file hello.lua, the following command should run it:

    prompt> lua hello.lua

As a slightly more complex example, the following program defines a function to compute the factorial of a given number, asks the user for a number, and prints its factorial:

    -- defines a factorial function
    function fact (n)
      if n == 0 then
        return 1
      else
        return n * fact(n-1)
      end
    end
    
    print("enter a number:")
    a = io.read("*number")        -- read a number
    print(fact(a))

If you are using Lua embedded in an application, such as CGILua or IUPLua, you may need to refer to the application manual (or to a "local guru") to learn how to run your programs. Nevertheless, Lua is still the same language; most things that we will see here are valid regardless of how you are using Lua. For a start, we recommend that you use the stand-alone interpreter (that is, the lua executable) to run your first examples and experiments.