<Ctrl-r>

In insert and command mode, <Ctrl-r> followed by a sequence inserts an object.

Insert mode usage mainly deals with manipulating registers. However, in command mode, <Ctrl-r><Ctrl-*> inserts special objects for certain *:

• F: Current filename under cursor

• P: Current filename with expanded path under cursor

• W: Word under cursor

• A: WORD under cursor

• L: Line under cursor

For more, :help c-^r.

Insert word under cursor

Very useful with :Ag, or when doing find/replace.

:Ag <Ctrl-r><Ctrl-w>
:%s/<Ctrl-r><Ctrl-w>/replacement-string