How to put the difference of two files in another file

Question

I have two files in two different buffers and I want to get the difference between these two files in another file

How can I do this with Vim?

Example:

BUFFER1

rtl.de
sat1.de
pro7.de
spiegel.de

BUFFER2

rtl.de
sat1.de
heise.de
pro7.de
spiegel.de

buffer3

heise.de

Answer 1

Vim offers a tool to see the difference between two buffers and put contents from one to another: diffthis (see :h :diffthis).

To get this diff mode you can either start it from the command line with:

$ vimdiff file1 file2

Or from within Vim:

• Open both of the buffers.
• create a split window to get both of the buffers on your screen. (with :split and :e for example)
• Start the diff mode with :windo diffthis
• Use :diffput and :diffget to modify the content of the buffers (:h :diffput and :h :diffget).
• Use :diffoff to stop the diff mode.

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Now to put the diff of the files in a third one I would recommend to use the diff from the (shell) command line with something like (See man diff):

$diff file1 file2 > file3

From within Vim you can get the result of this command in a buffer with:

:read !diff file1 file2

read allows to get the result of a command in the current buffer and ! allows to specify a string to be executed as an external command (here diff file1 file2)