Random strings in Lua

string.random.lua

math.randomseed(os.time())

local charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"

function string.random(length)
  if length > 0 then
    return string.random(length - 1) .. charset:sub(math.random(1, #charset), 1)
  else
    return ""
  end
end

local charset = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890"
math.randomseed(os.clock())
function randomString(length)
	local ret = {}
	local r
	for i = 1, length do
		r = math.random(1, #charset)
		table.insert(ret, charset:sub(r, r))
	end
	return table.concat(ret)
end

A small improvement over simplicity and speed

pseudo random, but super fast:

for i = 1, 10 do
	print( tostring({}):sub(10) )
end

40ae13c8
406c0640
41954060
41a91220
40ae1ac8
4195b718
41958260
41a3ea10
41a3acf0
41a3a978

local sets = {{97, 122}, {65, 90}, {48, 57}} -- a-z, A-Z, 0-9
local function string_random(chars)
	local str = ""
	for i = 1, chars do
		math.randomseed(os.clock() ^ 5)
		local charset = sets[ math.random(1, #sets) ]
		str = str .. string.char(math.random(charset[1], charset[2]))
	end
	return str
end

abc = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","r","s","t","u","v","z","y","w","q","1","2","3","4","5","6","7","8","9","0"}
local string = ""
function GeneratedString() 
    for i=1,35 do
        rdm = math.random(1,35)
        string = string..abc[rdm]
    end
    return string
end