This can be used to extract paths from evil-ex style paths. e.g. the
following inserts the stdout into the current buffer (assuming we're in
~/some/project/filename.c):
:R!echo %:P ~/some/project
:R!echo %:t filename.c
:R!echo %:e c
:R!echo %:r filename
:R!echo ~/another/project/%:t:r.h
~/another/project/filename.h
:R % contents of current file
http://vimdoc.sourceforge.net/htmldoc/cmdline.html#filename-modifiers
has a full list of vim filename modifiers. Doom doesn't support all of
them, but it does support most of them.
