Detailed explanation of Linux text processing tools

1. Count the number of users whose default shell is not /sbin/nologin in the /etc/passwd file, and display all users

grep is a text tool that processes text by matching it line by line;
Use the grep command with the -v parameter to display non-matching lines;
getent passwd | grep -Ev /sbin/nologin$

2. Find the username, UID and shell type of the user with the maximum UID value

Sort is used for sorting. Adding specific parameters can be used to sort according to different requirements;
head user takes the first few lines;
cut is used to extract specific columns;
sort -k3 -t“:” -rn uses colon as separator and sorts the numbers in the third column in reverse order;
cut -d ":" -f1,3,7 uses colon as separator and takes columns 1, 3, and 7;

3. Count the number of connections for each remote host IP currently connected to this machine and sort them from largest to smallest.

Ss can check the number of local connections, and use grep to filter the established sessions; use tr - to compress; use cut to intercept the corresponding columns; use sort to sort; and use uniq to remove duplicate statistics.

4. Write a script createuser.sh to implement the following functions: use a user name as a parameter, if the user with the specified parameter exists, display its existence, otherwise add it; display the ID number and other information of the added user;

Read variables through the read command;
Judge through test;
Conditional selection through if;
Specify the exit code through exit;

5. Write a script that generates the basic format of the script, including author, contact information, version, time, description, etc.;

Edit the contents of vim.rc in the user added directory, and add corresponding information when creating a .sh script file;

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