https://github.com/gmarik/vundle/blob/master/test/vimrc
My approach also works even if git doesn't exist (by skipping vundler).
I need this since sometimes I work on systems that don't have every bell-and-whistle I could want.
https://github.com/docwhat/homedir-vim/blob/master/vimrc/.vi...
if !isdirectory(expand(root, 1).'/vundle') exec '!git clone '.src.' '.shellescape(root, 1).'/vundle' endif
https://github.com/gmarik/vundle/blob/master/test/vimrc