How does the index affect the output of “git diff”?

Question

The index is the staging area right?

From the git docs:

git diff

Let's stop for a minute to see how the git diff command can be used to show you the difference between the version of a file in the working directory, index and most recent commit. The 3 main types of git diff commands you would likely use are:

git diff: Show differences between your working directory and the index.
git diff –cached: Show differences between the index and the most recent commit.
git diff HEAD: Show the differences between your working directory and the most recent commit.

My question is in regards to git diff . The thing is is that I didn't commit anything or git add anything yet and the changes in my working directory are shown when I type in git diff . My staging area is empty. when I type in git status , I see two files in red that will not be staged since I didn't use git add yet. So why does git diff show the changes I made in my working directory?

Answer 1

git diff: Show differences between your working directory and the index.

Working directory : your current code, even files that were not staged yet.

Index : You are right, this is the staging area.

When you do a git diff , it compares your current code with the staging area, which is precisely the behavior you described.

From the git documentation:

git diff

This form is to view the changes you made relative to the index (staging area for the next commit). In other words, the differences are what you could tell Git to further add to the index but you still haven't. You can stage these changes by using git-add[1].

So, we have 3 different situations:

1 - You have no changes not staged -> git diff shows nothing.

2 - You have some changes staged, some not staged -> git diff shows the diff between your CWD and staging area.

3 - Stage area empty, some changes -> git diff shows diff between CWD and the last commit.