I created a repo, created a file inside it, put some content in the file, and committed the file. Now, I'd like to see a diff of that commit, which should ideally show the file that was added and the lines that were added to it.
git diff HEAD^ HEAD
fatal: ambiguous argument 'HEAD^': unknown revision or path not in the working tree.
You can do:
git diff 4b825dc642cb6eb9a060e54bf8d69288fbee4904 HEAD
4b825dc642cb6eb9a060e54bf8d69288fbee4904 is the id of the "empty tree" in Git and it's always available in every repository.