Standard Variables
$0 ? calling function name
$N ? Nth command line argument value
$argv[N] ? same as above
$* ? all the command line arguments
$argv ? same as above
$# ? the number of command line arguments
$< ? an input line, read from stdin of the shell
$$ ? process number (PID) of the current process
$! ? process number (PID) of the last background process
$? ? exit status of the last task