Shell Variables

Variable	Description
$0	The name of the command being executed. For shell scripts, this is the path with which it was invoked.
$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.
$@	All the arguments are individually double quoted.
$?	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.