I’ve previously written about how to cut the current line without selecting it, using some custom lisp code. I’ve since noticed that my recommended setup, prelude already deals with this in a nicer way by using the package easy-kill. If you don’t use prelude, then install easy-kill and add
(global-set-key [remap kill-ring-save] 'easy-kill)
to your emacs config file.
Once you have done this, then
C-w with no region selected will cut (kill) the current line, and
M-w with no region selected will copy the current line. This is one of those neat shortcuts I use all the time and miss whenever I have to edit text outside of emacs!
The easy-kill package also offers the easy-mark function, that expands highlighted regions by word, line or other useful units, but I prefer expand-region for this purpose.