Linux represents the parent directory, the current directory, the root directory

/ refers to the root directory: it is the topmost directory of all directories
. / indicates the current directory

./ 一般需要和其他文件夹或者文件结合使用，指代当前目录下的东西
    cd . 没有太多意义
    cd ./文件夹   切换到当前目录的某个文件夹

...represents the parent directory

cd ..         切换到上级目录   
     cd ../文件夹    切换到上级目录中的某个文件夹

application:

tar compression
packs all jpg files in the directory into jpg.tar:

tar -cvf jpg.tar *.jpg

tar -cvf ../ILSVRC2012_img_train.tar *.tar
# 将当前目录下所有tar文件压缩到上级目录下，压缩后的文件名为ILSVRC2012_img_train.tar

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Reference link: CSDN blogger "Ordinary Netizen]; link: https://blog.csdn.net/m0_67401134/article/details/123973115