Shell script - "$"

$0

The name of the script being executed.

$1-$9

The first nine arguments of the script.

$#

The number of arguments passed to the script.

$*

All arguments of the script as a single string.

$@

All arguments of the script as an array.

$?

The exit status of the last executed command.

$$

The process ID of the current shell.

$!

The process ID of the last background command.

$-

Shows the current shell options or flags.