We have been using local variables, and explained that they are only available within their scope. Let's expand on what that exactly means.

local one = 1

if true then -- Code block starts
    local two = 2
    print(one, two) -- Output: 1, 2
end -- Code block ends

print(one, two) -- 1, nil

The local variable one is created outside of a codeblock, and therefore available in the entire file. The local variable two is created in an if-statement. In this if-statement, we can access both one and two. After the if-statement ends, two no longer exists. By indenting our code, we automatically visualize the scope of local variables.

As shown in the example below, you can create a local variable with the same name in a deeper scope level, without affecting the variable in the level above.

-- main.lua
a = 10 -- A global variable
require "example"
print(a) -- Output: 10
-- The global variable is unaffected by the local variable

-- example.lua
print(a) -- Output: 10
local a = 20 -- A local variable

function my_function(a) -- A parameter
    if true then
        local a = 40 -- Another local variable
        print(a) -- Output: 40
    end

    print(a) -- Output: 30
    -- The parameter is unaffected by the local variable
end

some_function(30)

print(a) -- Output: 20
-- The local variable is unaffected by the parameter

_G #

All global variables are actually part of the table _G.

animal = "whale"
print(_G.animal) -- Output: whale

_G.fruit = "apple"
print(fruit) -- Output: apple

This means that we can use _G to check out all the global variables.

animal = "whale"
fruit = "apple"

for k, v in pairs(_G) do
    print(k, v)
end
-- Output:
-- animal, whale
-- fruit, apple

In a later chapter we will learn how we can modify _G to prevent the creation of global variables.