A function to duplicate whatever the line under the cursor is. If you are a programmer this is something that you probably do a lot. However C-a C-k C-y C-y or C-a M-spc C-e M-w gets old very fast. Instead, put the following function in your .emacs:
(defun duplicate() "Duplicate it the line we are on" (interactive) (let ( (beg (line-beginning-position)) (end (line-end-position))) (copy-region-as-kill beg end) (beginning-of-line) (forward-line 1) (yank) (newline) (forward-line -1)))
and bind it to any key-kombo you like (I used C-c C-j), and duplicating lines is suddenly just a key press away.