How do I compare two files side by side using diff mode?

Explanation

The :diffthis command enables diff mode for the current buffer. Running it in two windows shows their differences highlighted.

How it works

1. Open two files in splits: :vsplit other_file
2. In the first window: :diffthis
3. Switch to the second window: <C-w>w
4. In the second window: :diffthis
5. Differences are now highlighted

Example

:vsplit file2.txt
:diffthis
<C-w>w
:diffthis

Tips

• :diffsplit filename opens a file and enables diff in one step
• ]c and [c jump between diff hunks
• do (diff obtain) pulls changes from the other window
• dp (diff put) pushes changes to the other window
• :diffoff disables diff mode
• :diffupdate refreshes after manual edits