I normally use git commit -a. I use git diff to preview my commit. However, recently I had to git add a file. After that, git diff didn't show the file, even th

I normally use git commit -a. I use git diff to preview my commit. However, recently I had to git add a file. After that, git diff didn't show the file, even though git commit did include it in the commit. So, it doesn't take long to realise that you need to understand the index after all. You need to learn git add -N, or use "git diff HEAD" instead of git diff.