Relative Line Numbers in Vim

.vimrc

set rnu
au BufEnter * :set rnu
au BufLeave * :set nu
au WinEnter * :set rnu
au WinLeave * :set nu
au InsertEnter * :set nu
au InsertLeave * :set rnu
au FocusLost * :set nu
au FocusGained * :set rnu

I found that this wasn't setting relative numbers when I would load a file, so I added a couple of events based on another commenter's post:

set rnu
au BufEnter * :set rnu
au BufLeave * :set nu
au WinEnter * :set rnu
au WinLeave * :set nu
au InsertEnter * :set nu
au InsertLeave * :set rnu
au FocusLost * :set nu
au FocusGained * :set rnu

Updated!

after applying this, you can't just set 'nonumber' in vim anymore (i.e to copy text into another application). you'll have to do the following:

set nu
set nonumber

Vim 7.4 introduced a hybrid mode that shows both relative number and the line number you're currently on. Now that either mode is non-exclusive I think you'll need to disable the current mode to toggle.

@brianbaligad is right. My current setup is:

set number
set relativenumber

augroup linenumbers
  autocmd!
  autocmd BufEnter *    :set relativenumber
  autocmd BufLeave *    :set number norelativenumber
  autocmd WinEnter *    :set relativenumber
  autocmd WinLeave *    :set number norelativenumber
  autocmd InsertEnter * :set number norelativenumber
  autocmd InsertLeave * :set relativenumber
  autocmd FocusLost *   :set number norelativenumber
  autocmd FocusGained * :set relativenumber
augroup END