1. Category of directory
The shell working directory.
The current directory which refers to the shell working directory.
HOME directory:
root : /root
Average user : /home/USERNAME
2. The cd command
Change the shell working directory / Change the current directory to DIR.
e.g :
cd or cd~ : Switch to the current user's home directory.
cd ~USERNAME : Switch to the home directory of the specified user.
cd - : Switch back and forth between the previous directory and the current directory.
. : The current directory.
.. : The parent directory of the current directory.
Environment variables related to the cd command:
PWD : Used to save the current directory.
The pwd command is used to read the value of the PWD environment variable.
OLDPWD : Used to save the previous directory.
That's why you can switch back and forth between the previous directory and the current directory.
cd- is equivalent to cd $OLDPWD.
3. The ls command : List contents of the specified directory.
Execution result of ls command with the option of -l :
-rw-r--r-- 1 root root 44800 Aug 14 14:32 install.log
The leftmost one : refers to the file type.
The next nine : refers to the file access authority.
The next digital 1 : The number of a file is hard linked.
the first root : The owner of the file.
the second root : The group of the file.
44800 : The size of the file.
Aug 14 14:32 : The last time the file was modified.
install.log : the file name.
1. mkdir
1.1 mkdir用来创建目录的：在这里目录和文件是一回是
[root@bogon tmp]# mkdir test/abc
如果test存在：创建成功
如果abc存在，则不会创建新的替换，且会报错。
如果test不存在：创建失败
-p, --parents : no error if existing, make parent directories as needed
[root@bogon tmp]# mkdir test/abc
如果test不存在,先创建test,后创建abc
如果abc存在，则不会创建新的替换，且不会报错。
-v, --verbose : print a message for each created directory
2. rmdir : remove empty directories
3. tree : list contents of directories in a tree-like format.