Is it possible to show all changes made to a buffer since the buffer was opened?

This question https://stackoverflow.com/questions/749297/can-i-see-changes-before-i-save-my-file-in-vim is related, but asks for changes since the last write, which can easily be accomplished by looking at the file on the file system.

I am using persistent undo (set undofile), so I cannot use :earlier <reallylargenumber>.

  • Why can't you use undo? Are you saying you haven't configured it to save enough entries? Then add more! :) I mean, that's Vim's change history mechanism after all.
    – B Layer
    Dec 30, 2018 at 15:14
  • :h DiffOrig provides a useful command for this
    – D. Ben Knoble
    Dec 30, 2018 at 15:51
  • @BLayer I don't know how far to go in the undo tree.
    – Bananach
    Dec 30, 2018 at 16:15
  • 1
    I guess you have to store highest undo sequence number from a autocmd on BufRead/BufReadPost using the function undotree(). Than you might be able to determine the value of for :earlier.
    – Ralf
    Dec 30, 2018 at 16:27
  • @D.BenKnoble Contrary to what the help text says this seems to diff to the last saved state (when I change a file then save with :w, and then run the command, it shows no change)
    – Bananach
    Dec 30, 2018 at 16:33

2 Answers 2


I played around. Could you try the following (rarely tested):

autocmd BufReadPost * let b:undo_seq_load=changenr()

function! DiffSinceLoad()
    let tmpa = tempname()
    let tmpb = tempname()
    let curchange=changenr()
    exe "undo " . b:undo_seq_load
    exec 'w '.tmpa
    exe "undo " . curchange
    exec 'w '.tmpb
    exec 'tabnew '.tmpa
    vert split
    exec 'edit '.tmpb
command! -nargs=0 DiffSinceLoad call DiffSinceLoad()

This is based on this answer.

Second iteration: This is now in my vimrc.

  • Use only one temporary file
  • If the buffer with the temporary file gets hidden, it is deleted.
  • When the buffer with the temporary file is deleted, :diffoff is called via autocmd.


" store the changenr at file load
autocmd BufReadPost * let b:changenr_on_load=changenr()
function! DiffSinceLoad()
    let tmpa = tempname()
    let curchange=changenr()
    exe "undo " . b:changenr_on_load
    exe 'w ' . tmpa
    exe 'undo ' . curchange
    exe 'vertical diffsplit ' . tmpa
    " when buffer gets hidden, delete it and reset diff settings
    setlocal bufhidden=delete
    autocmd BufDelete <buffer> diffoff
    " return to edited file
    wincmd p
command! -nargs=0 DiffSinceLoad silent call DiffSinceLoad()
  • I'm glad you understood what I needed. I'm currently wildly modifying my vimrc and sometimes just don't trust anything that was going on in my sessions.
    – Bananach
    Dec 30, 2018 at 17:04
  • @Bananach Great if I could help. If you find problems with this script (as said I didn't really test it), report here so we could improve the answer.
    – Ralf
    Dec 30, 2018 at 18:25
  • Is there a need for two temp files? If one side of the diff is the current state of the buffer in question I'd think you can just :split it (or :vert or whatever) and call :diffthis from the split window.
    – B Layer
    Dec 30, 2018 at 21:37
  • 1
    @BLayer See update.
    – Ralf
    Dec 31, 2018 at 1:19
  • Cool. Just FYI, you could combine the vsplit and two diffthis calls into a single command: exec "vert diffsplit ".tmpa.
    – B Layer
    Dec 31, 2018 at 20:22

This will do what you're looking for:

:w !diff % -
  • 1
    This shows the diffs since the last write, but not since loading the file.
    – Ralf
    Dec 30, 2018 at 16:28

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