Run the Last Command Again

!!

If you want to run the last command you used a second time, enter two exclamation points. That looks in the history file and runs the last command in the list.

$ pwd /home/scott $ !! pwd /home/scott 

Notice that you first see the actual command that's going to run, and then the results of that command. This is a truly useful way to have your computer do tedious work for you.