$$ Process ID of the shell’s own process $# Expands the number of parameters $0 Reference the name of the script $- Expands the script’s own parameters $? Returns the termination status of the last process $_ Absolute path of the script $@ Expands the parameters starting from 1 $* Same as $" but with double quotes !! Repeats the last command !$ Repeats the last argument of the last command