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Chapter 1. Getting Started
To keep with 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 or lua5.3— with the name of the text file that contains your program.
If you save the above program in a file hello.lua, the following command should run it:
% lua hello.lua
As a more complex example, the next 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("*n") -- reads a number
print(fact(a))
Chunks
We call each piece of code that Lua executes, such as a file or a single line in interactive mode, a chunk.
A chunk is simply a sequence of commands (or statements).
A chunk can be as simple as a single statement, such as in the “Hello World” example, or it can be composed
of a mix of statements and function definitions (which are actually assignments, as we will see later), such
as the factorial example. A chunk can be as large as we wish. Because Lua is used also as a data-description
language, chunks with several megabytes are not uncommon. The Lua interpreter has no problems at all
with large chunks.
Instead of writing your program to a file, you can run the stand-alone interpreter in interactive mode. If
you call lua without any arguments, you will get its prompt:
% lua
Lua 5.3 Copyright (C) 1994-2016 Lua.org, PUC-Rio
>
Thereafter, each command that you type (such as print "Hello World") executes immediately after
you enter it. To exit the interactive mode and the interpreter, just type the end-of-file control character
(ctrl-D in POSIX, ctrl-Z in Windows), or call the function os.exit, from the Operating System
library —you have to type os.exit().
Starting in version 5.3, we can enter expressions directly in the interactive mode, and Lua will print their
values:
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