$0, $? In Shell scripts? , $! , $, $ *, $ #, $ @, Etc.

$0, $? In Shell scripts? , $! , $, $ *, $ #, $ @, Etc.

$0 indicates the execution name of the program. The file name of the current script $ n indicates the nth parameter value of the program. n = 1 .. 9 $ * all parameters of this program. This option can contain more than 9 parameters. $ # Number of parameters of the program $ PID of the Program (ID of the current process running the script) $! Run the PID of the previous background command (ID of the last process running in the background) $? The Return Value of the last command (display the exit status of the last command. 0 indicates no error, and any other value indicates an error.) $-displays the current options used by shell. It has the same functions as the set command. $ @ is similar to $ *, but can be used as an array, when enclosed by double quotes (""), it is slightly different from $ *.