Level Up
Last month I tweeted about the progression one might see as he gets more comfortable in a terminal window (in my case, bash). Archived here, for posterity: repeating the last command you typed into bash.
Level 1, history via the up arrow:
$ <Up><CR>
Level 2, history without the arrow:
$ <C-P><CR>
Level 3, parameter expansion:
$ !!<CR>
Level 4, loop that waits for enter key:
$ while true ; do cmd ; read foo ; done
Bonus Level 5, loop that waits for filesystem event:
$ while true ; do inotifywait -e modify filename ; cmd filename ; done