[qwertyuiop924]

...Which is actually quite simple. Here's my function for doing that that I wrote just now:

  (defun duplicate-line 
    (interactive)
    (kill-whole-line)
    (yank)
    (yank))

Five lines, and it took me all of ten minutes to write, including looking up the names of all the functions. Of course, there's probably a better way to do this, but I don't know what it is. Now all you have to do is bind it to a key.

Or, of course, you could just record a keyboard macro to do it instead.

[_asummers]

I have mine set up like this:

https://gist.github.com/asummers/7784d40b1bc53ee309777274e9d...

That way I can hit M-w when I don't have a region and get the copy behavior for the whole line.

[qwertyuiop924]

That's cool. I have no idea how that works, but it's cool.