How do I see changes in the git index?

Question

Say I do

git add foo.txt

Now, foo's changes are in the index (I'm assuming git was already tracking that file). Now, when I do git diff, I can't see the changes in foo by doing

git diff

Are there some extra things that git diff wants before it shows me those changes?

Answer 1

git diff shows unstaged changes. To get the staged/cached changes, you can do git diff --cached. To get both cached and uncached changes, you can do git diff HEAD, which compares the whole working tree to the named commit (HEAD).