How do I save the changes to my vim buffer as a patch file?

Question

Is there a way to save the changes I made to my vim buffer as a patch file for the original file, without saving it as a separate file and using diff?

Answer 1

It's possible to do this without a plugin using the w command, so the buffer contents can be used in a shell command:

:w !diff -au "%" - > changes.patch

(% is substituted with the path of the file being edited, - reads the buffer from stdin)

Answer 2

You could also filter the buffer through diff using the %! syntax:

:%! diff -au "%" -

This will fill the buffer with the diff, rather than writing it to disk; you may want to set readonly so you don't clobber the original by accident (OTOH, that shouldn't be a serious problem because you have the file under version control, right?). Of course, it helps to have the inverse command:

:%! patch -o - "%"

That transforms your diff back into the modified file.