vimdiff allows you to diff and merge two files in vim. Start it with either of the following commands:
vimdiff [file1] [file2]
vim -d [file1] [file2]
You can also use gvim, in which case substitute "vim" for "gvim" in the above commands.
If you are already in vim (editing [file1]), use the following command to do a vertical diff between the current file and another.
:vert diffsplit [file2]
If you want to use the --remote-tab or --remote-tab-silent switch to open the diff in a new tab in the existing window, you need to start the diff via a command rather than via a switch:
vim --remote-tab-silent -c "vert diffsplit [file2]" [file1]
Note that you will need to escape any spaces in [file2].
Scrolling
To get both files scrolling at the same time I had to set the scrollbind option in my .vimrc file (or set it in /etc/vim/vimrc as a global setting):
set scrollbind
Redoing the diff
If you loose the diff for whatever reason (e.g. I lost the diff when opening a new tab with :tabnew), turn the diff option on again.
:set diff
You'll also need to redo the diff if you make a non-trivial change to a line, in which case run the following:
:diffupdate
Moving around
Switch viewport:
ctrl-w w
Jump to next diff:
]c
Jump to previous diff:
[c
Merging
Whole diff
To replace a diff in the current viewport with that from the other viewport, use the :diffget command. This can be shortened to the following:
do
To replace a diff in the other viewport with that from the current viewport, use the :diffput command. This can be shortened to the following:
dp
If you want to get contents from the other viewport when the current viewport has "filler" - i.e. a series of dashes - then do so from the line below.
Part of the diff
To replace just a single line or multiple lines in a diff in the current viewport (rather than getting the entire diff), use a range. You have to use the full command for this - you can't use the shortened command shown above. For example, if you want to get line 63 from the other viewport, do the following:
:63diffget
The diffget command can be shortened slightly to diffg.
It's similar for diffput.
