Shell $ variable

$0: The current script has a file name of $num:num 1-based number,$ $ is the first argument, and $ is the second argument, and ${is thetenth argument $#: The number of arguments passed in the script $* : All positional parameters (as a single string) [email protected]: all positional parameters (each as a separate string). $?: The return value of the previous command in the current shell process, or $ if the previous command executed successfully? the value of 0, otherwise not 0 value, commonly used to do if statement conditions $$: The current shell process pid$! : pid$ of the last process running in the background-: Shows the current options used by the shell $_: The last parameter of the previous command

Shell $ variable