The implementation of this program name $ 0
$ n the n-th program of parameter values, n = 1..9
all the parameters of this program $ * This option can be more than nine parameters.
$ # Number of arguments in this program of
$$ this program's PID (script running current process ID number)
$! PID (last process running in the background on the implementation of a directive of the background process ID number)
$? Instruction on execution the return value (final command to display the exit status of 0 means no error, any other value indicates an error)
$ - displays the current use of shell option, and set the command functions the same
$ @ $ * with a similar, but can be used as an array
