Lua: string.sub a string too long

Append to the end of a string that is larger than the value of x where x is the maximum length and position of where the string should be appended.

value = string.sub(value, 1, length - 1) .. "..." end

Example:

local value = "This is a long string that needs substitution."
local maxLength = 12

if #value > maxLength then value = string.sub(value, 1, maxLength - 1) .. "..." end