How do I see a diff of my unsaved changes compared to the version on disk?

Explanation

The command :w !diff % - pipes the current buffer's contents to an external diff command that compares it against the saved file on disk. This lets you review exactly what you have changed since the last save — without needing to write to a temp file or open a new split.

How it works

• :w !cmd — writes the buffer contents to standard input of cmd rather than to disk
• diff % - — runs diff with two arguments: % expands to the current file's path (the on-disk version), and - reads from standard input (the unsaved buffer)
• The output is a standard unified diff showing added and removed lines

Example

You open config.lua, change timeout = 300 to timeout = 600, and add a new line. Before saving:

:w !diff % -

Output:

3c3
< timeout = 300
---
> timeout = 600
5a6
> new_option = true

Tips

• For a more readable unified diff with context lines:

  :w !diff -u % -
  

• Add it as a command mapping in your vimrc so it is always at hand:

  command! DiffSaved w !diff -u % -
  

• If diff is not available, use git diff for files inside a git repo: :!git diff %
• Neovim users can also use vim.diff() via Lua, but :w !diff % - works in both Vim and Neovim without configuration
• This is especially useful in CI-like environments or when reviewing changes before a :wq