Shell Script 1

 Shell Variable     Description
$0     The filename of the current script.
$n     These variables correspond to the arguments with which a script was invoked. Here n is a positive decimal number
    corresponding to the position of an argument (the first argument is $1, the second argument is $2, and so on).
$#     The number of arguments supplied to a script.
$*     All the arguments are double quoted. If a script receives two arguments, $* is equivalent to $1 $2.
$@     All the arguments are individually double quoted. If a script receives two arguments, $@ is equivalent to $1 $2.
$?     The exit status of the last command executed.
$$     The process number of the current shell. For shell scripts, this is the process ID under which they are executing.
$!     The process number of the last background command.