File renamer

fs.rename = fs.move

local function digits(str)
  local a, b
  local c, d
  for i = 0, #str do
    c, d = a, b
    a, b = str:find(string.rep("%d", i))
    if not a then
      break
    end
  end
  return c, d
end

local function split(str)
  local a, b = digits(str)
  local prefix = str:sub(1, a - 1)
  local digits = tonumber(str:sub(a, b))
  local zerocount = (b - a + 1) - #tostring(digits)
  local suffix = str:sub(b + 1, #str)
  return prefix, digits, zerocount, suffix
end

local function add(str, val)
  local data = {split(str)}
  data[2] = tostring(data[2] + val)
  local name = data[1]..string.rep("0", data[3])..data[2]..data[4]
  return name
end

function renameFiles(val, loc)
  local loc = loc or "/rename"
  if not fs.exists(loc) then
    error("Location folder ("..loc..") doesn't exists", 2)
  for _, oldName in pairs(fs.list(loc)) do
    if not fs.isDir(oldName) then
      local newName = add(name, val)
      fs.rename(oldName, newName)
      print("Renamed "..oldName.." to "..newName..".")
    end
  end
end