$ @ And other meanings of specific shell variables

Article Title: $ @ and other meanings of specific shell variables. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.
In the actual writing of shell scripts, some special variables are very useful:
1. $ # number of parameters passed to the script
2. $ * display all parameters passed to the script with a single string. Different from location variables, this option can have more than 9 parameters
3. $ ID of the current process running the script
4. $! ID of the last process running in the background
5. $ @ is the same as $ #, but it is enclosed by quotation marks and each parameter is returned in quotation marks.
6. $-display the current options used by shell, which have the same functions as the set command.
7. $? Displays the exit status of the last command. 0 indicates no error, and any other value indicates an error.