Global variables

A global variable can be accessed in every scope and can be modified from anywhere. The term scope is used to describe the area in which a set of variables live. You don't have to declare a global variable. It is created as soon as you assign a value to it.

myVariable = 10
print( myVariable )  -- prints the number 10

Local variables

A local variable is accessed from a local scope and usually called from a function or block of code. When we create a block, we are creating a scope in which variables can live or a list of statements, which are executed sequentially. When referencing a variable, Lua must find the variable. Localizing variables helps speed up the look-up process and improves the performance of your code. By using the local statement, it declares a local variable.

local i = 5  -- local variable

The following is how to declare a local variable in a block:

x = 10    -- global 'x' variable
local i = 1
 
while i <= 10 do
   local x = i * 2  -- a local 'x' variable for the while block
   print( x )       -- 2, 4, 6, 8, 10 ... 20
   i = i + 1
end
 
print( x )  -- prints 10 from global x

Table fields (properties)

Table fields are elements of the table themselves. Arrays can be indexed with numbers and strings or any value pertaining to Lua except nil. You index into the array to assign the values to a field using integers. When the index is a string, the field is known as a property. All properties can be accessed using the dot operator (x.y) or a string (x["y"]) to index into a table. The result is the same.

x = { y="Monday" }  -- create table 
print( x.y )  -- "Monday"
z = "Tuesday"    -- assign a new value to property "Tuesday"
print( z )  -- "Tuesday"
x.z = 20  -- create a new property 
print( x.z )  -- 20
print( x["z"] )  -- 20

More information relating to tables will be discussed later in the section called Tables.

You may have noticed the additional text on certain lines of code in the preceding examples. Those are what you call comments. Comments begin anywhere with a double hyphen -- , except inside a string. They run until the end of the line. Block comments are available as well. A common trick to comment out a block is to surround it with --[[.

Here is how to comment one line:

a = 2
--print(a) -- 2

The following is a block comment:

--[[
k = 50
print(k)    -- 50
]]--

Assignment conventions

There are rules for variable names. A variable starts with a letter or an underscore. It can't contain anything other than letters, underscores, or digits. It also can't be one of the following words reserved by Lua:

The following are valid variables:

The following are invalid variables: