计算文件夹下内容大小
命令:du -shL [文件夹名] 详细解释: -s display only a total for each argument 仅显示总计，列出最后加和的值-h print sizes in human readable format (e.g., 1K 234M 2G) 以K,M,G为单位，提高可读性-L dereference all symbolic links 显示符号链接的源文件大小