git add --patch a lot.
In VSCode's Source Control Tab,
you can double-click on the staged file,
and a split screen will open up with the changes side-by-side.
But how to do this in the terminal?
git diff --staged.
You can also use
git diff --cached.
git diff --help says:
git diff [<options>] --cached [<commit>] [--] [<path>...] This form is to view the changes you staged for the next commit relative to the named <commit>. Typically you would want comparison with the latest commit, so if you do not give <commit>, it defaults to HEAD. If HEAD does not exist (e.g. unborn branches) and <commit> is not given, it shows all staged changes. --staged is a synonym of --cached.