$# Stores the number of command-line arguments that were passed to the shell program.
$? Stores the exit value of the last command that was executed.
$0 Stores the first word of the entered command (the name of the shell program).
$* Stores all the arguments that were entered on the command line ($1 $2 ...).
"$@" Stores all the arguments that were entered on the command line, individually quoted ("$1" "$2" ...).
$$ is the process ID (PID) of the script itself.
Note :
"$@" is
individually quoted ("$1" "$2" ...).
