As per my understanding git diff is used to compare files between Working Directory and Staging Area. However, If I have no staged changes in the Staging Area, the same command git diff compare files between Working Directory and HEAD.

Why the same command (git diff) is giving two different outputs?

How do I actually diff between Working Directory and Staging Area?

CodePudding user response：

First, one point needs clarification :

In git, when one talks about files in "the staging area" or "the index", they actually refer to :

• the files as they are in the HEAD commit,
• plus the potential git added modifications.

So the meaning of "there are no modifications in the staging area" is :
"the staging area is the same as HEAD".

With that in mind, you can re-read the diagram posted by VonC :

• git diff will display the differences between the worktree and the staging area (the index) ;
• when there are no extra modifications staged, "the index" is the same as HEAD -- as a consequence, git diff will indeed show the difference between HEAD and your worktree ;
• the command that will always show you "the difference between HEAD and your worktree" (and disregard the index) is : git diff HEAD