Question

I use Vim.
I open a file. I edit it and I want to see what I’ve edited before I save it.

How can I do this in Vim?

Answer 1

http://vim.wikia.com/wiki/Diff_current_buffer_and_the_original_file

Here is a function and command to see a diff between the currently edited file and its unmodified version in the filesystem. Just put this in your vimrc or in the plugin directory, open a file, make some modifications without saving them, and do :DiffSaved.

function! s:DiffWithSaved()
  let filetype=&ft
  diffthis
  vnew | r # | normal! 1Gdd
  diffthis
  exe "setlocal bt=nofile bh=wipe nobl noswf ro ft=" . filetype
endfunction
com! DiffSaved call s:DiffWithSaved()

To get out of diff view you can use the :diffoff command.

Below is a similar function, adapted to mimic the 'cvs diff' command…