Lua判断一个目录或文件是否存在的方法

file,err=io.open("XXXX")

somefile="xxxj.pdf"
local F,err=io.open(somefile,"r+");
print(err)

function file_exists(path)
  local file = io.open(path, "rb")
  if file then file:close() end
  return file ~= nil
end