$ expands to the process ID of the shell. So, you can see the PID of the current shell with echo $$.
Adding | pbcopy to the end of any command will send the standard output to your clipboard.
If you are working with a complicated command in the terminal trying to get the arguments just right. Such as this curl:
Recently while trying to fix a printer I used lpr a bunch of times. It’s not exactly new to me, but never fails to surprise people when I use it.
The last command is a handy way to find out who has been connecting to a machine and when.