• $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.