What are the differences between these git diff commands?

Question

What are the differences between the following git commands?

1. git diff HEAD
2. git diff HEAD^
3. git diff --cached

Answer 1

From the Git Community Book:

git diff

will show you changes in the working directory that are not yet staged for the next commit.

git diff --cached

will show you the difference between the index and your last commit; what you would be committing if you run "git commit" without the "-a" option.

git diff HEAD

shows changes in the working directory since your last commit; what you would be committing if you run "git commit -a".