随机字符串

local Chars = {}
for Loop = 0, 255 do
   Chars[Loop+1] = string.char(Loop)
end
local String = table.concat(Chars)

local Built = {['.'] = Chars}

local AddLookup = function(CharSet)
   local Substitute = string.gsub(String, '[^'..CharSet..']', '')
   local Lookup = {}
   for Loop = 1, string.len(Substitute) do
       Lookup[Loop] = string.sub(Substitute, Loop, Loop)
   end
   Built[CharSet] = Lookup

   return Lookup
end

function string.random(Length, CharSet)
   -- Length (number)
   -- CharSet (string, optional); e.g. %l%d for lower case letters and digits

   local CharSet = CharSet or '.'

   if CharSet == '' then
      return ''
   else
      local Result = {}
      local Lookup = Built[CharSet] or AddLookup(CharSet)
      local Range = #Lookup

      for Loop = 1,Length do
         Result[Loop] = Lookup[math.random(1, Range)]
      end

      return table.concat(Result)
   end
end