====== diff ======
To perform a 'diff' is to view the differences between two files.  Vim will automatically show you the different areas by highlighting the lines.  You can easily copy those portions between the files if desired.

===== diff from command line =====
diff's are so common that vim comes with a command just for them.  To start vim in diff mode with two files, use the vimdiff command:
<code>
vimdiff <file1> <file2>
</code>

===== diff after vim is started =====
If vim is already running, open the first file.  Type the following (command mode):
<code>
:diffsplit file2
</code>

===== diff preferences =====
You can adjust your .vimrc file to customize your diff usage.  A common viewing preference is to make diff's show up vertically, instead of horizontally.

<code>
" make vertical the default diff split (filler was already there)
set diffopt=filler,vertical
</code>

Winmerge is a popular Windows-only application, dedicated to managing diffs.  You can simulate the behavior of the Winmerge keys with the following:
<code>
" disable cmd opt mappings for MacVim (interferes with winmerge mappings)
let macvim_skip_cmd_opt_movement = 1

" use diff navigation like winmerge, using alt with up, down, left, right
nnoremap <M-Down> ]c
nnoremap <M-Up> [c
function! CopyToLeft() 
	if !&diff
		return
	endif

	let currwin = winnr()
	if( currwin == 1 )
		:diffget
	else
		:diffput
	endif
endfunction
function! CopyToRight()
	if !&diff
		return
	endif

	let currwin = winnr()
	if( currwin == 1 )
		:diffput
	else
		:diffget
	endif
endfunction
nnoremap <M-Right> :call CopyToRight()<CR>
nnoremap <M-Left> :call CopyToLeft()<CR>
</code>

===== diffs on directories (multiple files) =====
Vim by default only handles diffs between files.  If you need to analyze entire directories, try using the [[docs:diff:dirdiff|DirDiff]] plugin for vim.