Using Vim's persistent undo?

Question

One of the new features in Vim 7.3 is 'persistent undo', which allows for the undotree to be saved to a file when exiting a buffer.

Unfortunately, I haven't quite been able to get it properly enabled, or I must be using it wrong. Here's what I've tried so far:

I added the following to ~/.vimrc

set undofile                " Save undos after file closes
set undodir=$HOME/.vim/undo " where to save undo histories
set undolevels=1000         " How many undos
set undoreload=10000        " number of lines to save for undo

After this, I supposedly should be able to open any file, edit it, then save-close it, and when I open it again I should be able to undo/redo as if I'd never left. Unfortunately, this doesn't seem to be the case, as no undofile is ever written.

Notes:

1. I'm on Win 7 using Vim 7.3 from the Vim without cream project. Persistent undo is baked-in.

2. $HOME/.vim/undo exists on my file system

Interlunar

Just to stress, point 2) is very important. Vim will not create the directory for you and persistent undo will not work until you mkdir ~/.vim/undo – Manhood

+1. Sorry, on Linux it works... thanks for telling me about it! – Pettifogger

For any future visitors to this question: Do NOT put quotes around the value of undodir! I got stuck on this problem for a while - use an absolute paht, without quotes around it. – Cordellcorder

Answer 1

Put this in your .vimrc to create an undodir if it doesn't exist and enable persistent undo. Tested on both Windows and Linux.

" Put plugins and dictionaries in this dir (also on Windows)
let vimDir = '$HOME/.vim'

if stridx(&runtimepath, expand(vimDir)) == -1
  " vimDir is not on runtimepath, add it
  let &runtimepath.=','.vimDir
endif

" Keep undo history across sessions by storing it in a file
if has('persistent_undo')
    let myUndoDir = expand(vimDir . '/undodir')
    " Create dirs
    call system('mkdir ' . vimDir)
    call system('mkdir ' . myUndoDir)
    let &undodir = myUndoDir
    set undofile
endif

Tunnage

This may be preferable for creating the directory: :silent call system('mkdir -p ' . &undodir) – Serology

I use & because I set the undodir rather than letting it. (In my mind this distinction between let and set is one of the many, many, many mind-bogglingly awful "features" of Vimscript, but YMMV.) – Serology

Thanks Kyle, it's a good idea to create .vim if it doesn't exist. Unfortunately the -p flag doesn't exist on Windows so I edited the answer to call mkdir twice to ensure Windows compatibility. – Tunnage

Ah. My primary reason for using the -p flag is actually to avoid an error when the directory exists. I have my command inside an if has('win32') block, so I just use mkdir without -p on Windows. – Serology

Why not use mkdir()? Then this can become: call mkdir(myUndoDir, 'p'), which behaves like mkdir -p. – Geostatic

Thanks for the hint, @nelstrom. call mkdir(myUndoDir, 'p') gives me an error (probably because the directory already exists): Cannot create directory: C:\Users\me\.vim\undodir – Tunnage

@MatthiasBraun I just realised that the documentation for mkdir() is different in Vim and Neovim. When I suggested this I had been looking at Neovim's documentation, which states that: "If you try to create an existing directory with {path} set to "p" mkdir() will silently exit.". Apparently this is not the case in Vim. My bad! – Geostatic

@Geostatic That's an excellent modification. Thanks. (The answer to your "why not" question is "because I didn't know that existed.") – Serology

Related: How can I create a folder, if it doesn't exist, from .vimrc?. – Havstad

Answer 2

I tried this in my _gvimrc:

" Persistent undo
try 
    set undodir=C:\vim\undodir
    set undofile
catch
endtry

It started working as advertised when I deleted the try-catch bracket, thus:

" Persistent undo
set undodir=C:\vim\undodir
set undofile

I had to create the directory.

Bonnette

if has('persistent_undo') – Lunt

silent !mkdir ~/.config/nvim/backups > /dev/null 2>&1 – Lunt

set undodir=~/.config/nvim/backups – Lunt

endif " adding commented message to increase message length – Lunt

What is the point of has('persistent_undo')? Why do I need it? When is it true? When is it false? – Lira

has('persistent_undo') returns true if the vim instance it's running on was compiled with the persistent undo option. It's useful in case you use the same vimrc in diverse environments. – Bonnette

Answer 3

I suppose $HOME doesn't work as advertised.

On my system, :echo $HOME shows H:\, but : e $HOME/ says: ~/ invalid filename.

You could try with an absolute path to see whether it cures it

Myeshamyhre

I could |:echo $HOME| and |:e $HOME/| without problems, but I tried changing things anyways. It seemed to work at times, and not at others. Particularly, it never saves backups when I'm editing my ~/.vimrc file. – Interlunar

On windows 7 I'm using $TEMP. When I look set undodir? it shows ~/AppData/Local/Temp. Undo file is persisted and loads itself correctly. Maybe $TEMP will be more reliable? – Agar

In linux ~ is a shortcut for $HOME in the commandline, as you already know. About it working sometimes, I guess that it might depend on which environment you start vim from. I imagine that it would work inside the mini shell that comes with git installations, but might not be recognized in a plain Windows shell. Cannot test, don't run Windows any more. Perhaps with H:\ ... – Bonnette

Answer 4

This now works as expected: file.txt open in a Vim 7.4 buffer on Windows 7, :setlocal undofile, then save a change to the buffer, and the undofile .file.txt.un~ is created alongside because :set undodir? reports that "undodir=." by default - ie no need to specify this manually. You can also :set undofile in a modeline.

Biestings