Lua Academy · Lesson

Declaring Variables in Lua

Understand global vs local variables and naming conventions.

Global vs Local Variables

In Lua, variables are global by default. Writing x = 10 without the local keyword creates a global variable accessible from anywhere. Using local x = 10 restricts the variable to the current block and its nested blocks.

Always prefer local for performance and safety. Accessing a local variable is faster than a global because globals require a hash table lookup in the _G table.

x = 100          -- global variable
local y = 200    -- local variable

do
  local z = 300  -- block-local
  print(x, y, z) -- 100  200  300
end

print(x, y)      -- 100  200
print(z)         -- nil  (out of scope)

The local Keyword

The local keyword declares a variable scoped to the nearest enclosing block: a function body, a do...end block, a loop body, or a file chunk. Local variables are created at the line they're declared and cease to exist at the end of their block.

You can declare multiple locals on one line and initialize them simultaneously. Uninitialized locals default to nil.

local a, b, c = 1, 2, 3
print(a, b, c)    -- 1  2  3

local d, e = 10   -- e is nil
print(d, e)       -- 10  nil

local f           -- nil until assigned
f = 42
print(f)          -- 42

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