When using the C shell, I use
much that it's almost a single character to me.
It means "take the last thing on the previous command line."
It works on bash too.
Since most UNIX commands have the filename last, you often need to type
filenames only once, and then you can use
!$ in subsequent lines.
Here are some examples of where it comes in handy:
tar xvf !$tar xvf groff.1.05.tar
spell !$spell fred.letter.txt
mv grmacs.tar /usr/lib/tmac%
cd !$cd /usr/lib/tmac