Given a modified buffer, how can I diff it with the file backing it on disk to see what I've changed?
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Related/Duplicate: How to view diff when emacs suggests to recover this file?– Kaushal ModiJan 17, 2015 at 17:11
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There has been the same question at unix.stackexchange.com, but with less asnwers.– imz -- Ivan ZakharyaschevJan 24, 2015 at 10:00
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2 Answers
You want the command M-x diff-buffer-with-file. See the manual:
diff-buffer-with-file is an interactive autoloaded compiled Lisp function in `diff.el'.
(diff-buffer-with-file &optional BUFFER)View the differences between BUFFER and its associated file. This requires the external program
diffto be in yourexec-path.
You may also be interested in highlight-changes-mode which automatically and interactively highlights changes made to the buffer after it was enabled.
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Along the lines of
highlight-changes-modethere's also thediff-hlpackage in GNU ELPA.– StefanJan 17, 2015 at 4:00 -
1Yes, but right now it only works to show diffs between the (saved) buffer and a
vcrevision. I worked on diffing the buffer (as opposed to its backing file) in diff-hl #33, but it's blocked on a bug in the Emacs core. Jan 17, 2015 at 5:27 -
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Command ediff-current-file:
ediff-current-file is an interactive autoloaded Lisp function in
`ediff.el'.
(ediff-current-file)
Start ediff between current buffer and its file on disk.
This command can be used instead of `revert-buffer'. If there is
nothing to revert then this command fails.
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ediff-current-filehas some benefits overdiff-buffer-with-fileif you want interactive review of changes rather than a plain diff. The interactive review even allows to selectively revert some parts, in case you finally don't want to save them. See also emacs.stackexchange.com/a/3778/10614 for a more complete answer. Dec 29, 2015 at 11:20