Command-line
sudo apt-get install ack-grep
sudo dpkg-divert --local --divert /usr/bin/ack --rename --add /usr/bin/ack-grep
.vimrc
nnoremap <leader>a :Ack
" Search for word under cursor
nnoremap <leader>A :Ack <C-r><C-w>
" Fix for Ack < 2.0
let g:ack_default_options = " -H --nocolor --nogroup --column"