Vim: use the path of the current file
Answered at https://stackoverflow.com/questions/2233905/howto-get-full-path-of-current-file-in-vim
% is the actual file
%:p:h
is the dirname of the file
%:p
is the full path of the file. Use what you prefer.
In order to save files, just
:w %:p:h/something