1. Take out line 6 of the /etc/passwd file;
2. Take out the shells of all users on the current system. It is required that each shell is only displayed once and displayed in order;
Use cut, sort combined with pipeline implementation
pass: sort is for sorting - u is for deduplication
3. If the number of lines in the /var/log/messages file is greater than 100, it will display a very large file
4. Display all files starting with pa in the /etc directory, and count their numbers
5. If the user hadoop does not exist, add it, otherwise it will display that the user already exists
6. Write a shell program mkf. The function of this program is: display the file information under root, then create a kk folder, create a file aa under this folder, and modify the permission of this file to be executable
7. Write a shell program test3, read a directory name from the keyboard when the program is executed, and then display the information of all files in this directory
8. Write a shell program test4, read the values of x and y from the keyboard, then do addition, and finally output the result
