The undo command is a lifesaver when you need to revert changes that didn’t work out. Typically, you can only undo changes that were made to a file during the current editing session. By enabling Vim’s ‘undofile’ option, you can make undo history persist between editing sessions.

Open the green-bottles.txt file from the source code that accompanies this book in Vim:

Use the <C-x> command to decrement the number at the start of the line. Now you can use u to undo the change and <C-r> to redo it. If you quit Vim and then reopen the same file, what do you expect to happen when you use the u command?

Your undo history is usually lost when you quit your text editor. If you enable the ‘undofile’ option, then Vim will write your undo history to a hidden file, making it persist between editing sessions (:help persistent-undo). To enable this feature, add this line to your vimrc file then reload it:

Switch back to the green-bottles.txt file and use the <C-x> command again to decrement, then for good measure, use . a couple of times to repeat the change. Now quit Vim and reopen the same file. You should be able to use u to undo those changes. Pretty cool, huh?

Saving Undo Files in a Designated Directory

With the ‘undofile’ option enabled, Vim records the undo history for a file by writing to a hidden file in the same directory. In the previous example, the green-bottles.txt file would have its undo history written to a file called .green-bottles.txt.un~. This can lead to a proliferation of hidden files mixed into your working directory.

To avoid this, use the ‘undodir’ option to specify a directory where your undo files will be saved. Add this line to your vimrc, then reload your vimrc:

If the path specified in ‘undodir’ doesn’t exist, then persistent undo won’t work. Create the directory by running:

If you’re using Neovim, you can stick with the default ‘undodir’ value of $XDG_DATA_HOME/nvim/undo. You’ll still have to create the directory, though.

Disabling Persistent Undo for Temporary Files

Persistent undo is an appealing feature, but it brings some security concerns. Suppose you are using a password manager that uses $VISUAL to launch your preferred text editor. You wouldn’t want to leak your secure password in the form of a hidden undo file.

To avoid this situation, use an autocommand to disable ‘undofile’ locally for files that match a particular pattern. For example, here’s how to disable persistent undo for all files in the /tmp directory:

You can tweak the file pattern to suit your needs. If you are not familiar with Vim’s autocommands, read Tip 26, ​Using Autocommands to Respond to Events​ for an introduction.

Putting It All Together

Copy this snippet into your vimrc whether you’re using Vim or Neovim:

This enables persistent undo (except for temporary files) and saves undo files to a designated directory.