I don't see a difference between the output of 'git format-patch' and 'git diff', is there any? And won't I be able to use 'git diff' to produce a patch and then apply it using git apply?

My problem is that I have changes added to the index, but apparently git format-patch only accepts commits, so if I can use the output of diff, then I can use this command to produce a patch for the changes in the index:

git diff --cached > index.patch
git diff patch
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