random_string.lua

function string.random(length)
  if length < 1 then return nil end

  local str = ""

  for i = 1, length do
    n = math.random(32, 122)
    if (n > 32 and n < 48) or (n > 57 and n < 65) or (n > 90 and n < 97) then n = math.random(97, 122) end
    str = str .. string.char(n)
  end
  return str
end

print(string.random(100))