1. PWD shows the current folder you are working on.

2. Type cd / to go to the root dictionary.

3. Absolute route (cd /home/dq) vs. relative path (cd home).

4. Type whoami to check the current username.

5. Type cd ~ to go back to the user folder.( home directory)

6. Type mkdir test to create a test folder in the current directory.

7. -v is an opinion of a command, and the function is to show the detail of the command.

8. mkdir --help is to understand all the possible opinions of mkdir

9. ls is to show all the directory, ls -l is to show all the detailed directory.

10. We use rmdir to delete the dirtectory.

11. touch test.txt is to create a file named test.txt. touch command can also updata/modify files.

12. 

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