Shell knowledge record

Shell knowledge record Shell automatic variables: [plain] $ # number of parameters passed to the script $ * display all parameters passed to the script in a single string. Different from the location variable, this option parameter can contain more than 9 $ PID Number of the current process running the script $! The process Number of the last process running in the background $ @ is the same as $ *, but double quotation marks are used, and each parameter is added with double quotation marks to return $-display the current options used by shell, similar to the set command, $ _ the last parameter of the previous command $? The exit status of the last command is displayed. 0 indicates that the execution is successful. If other values are incorrect, $0 indicates that the script name is $1... $9.