What are the differences between these git diff commands?

Solution 1:

1. git diff HEAD - Shows what has changed since the last commit.
2. git diff HEAD^ - Shows what has changed since the commit before the latest commit.
3. git diff --cached - Show what has been added to the index via git add but not yet committed.
4. git diff - Show what has changed but hasn't been added to the index yet via git add.

It looks like this:

     Working
    Directory  <----+--------+------+
        |           |        |      |    
        |           |        |      |
        V           |        |      |    
    "git add"       |        |      |    
        |         diff       |      |    
        |           |        |      |    
        V           |        |      |    
     Index     <----+    diff HEAD  |            
        |           |        |      |       
        |           |        |      |
        V           |        |      |       
  "git commit"      |        |      |
        |     diff --cached  |      |
        |     diff --staged  |      |
        V           |        |      |
      HEAD     <----+--------+      |
        |                           |
        |                        diff HEAD^
        V                           |
previous "git commit"               |
        |                           |
        |                           |
        V                           |
      HEAD^    <--------------------+

Solution 2:

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".

Solution 3:

1. git diff HEAD : Diff between HEAD and the working directory.
2. git diff HEAD^ : Diff between the direct ancestor of HEAD and the working directory.
3. git diff --cached or the synonym git diff --staged : Diff between HEAD and the index.
4. git diff : Diff between the index and the working directory.

Solution 4:

Here's a simple way to remember these commands:

• By default, git diff's source is assumed to be the working directory, and its target is the index.
• Adding the --cached flag changes the source to be the index. It doesn't necessarily change the target once you add more arguments. But for convenience the target becomes the last commit if none is provided.
• Adding a commit as an argument changes the target.
• Adding two commits as arguments changes both the source and the target, respectively.

Have fun mixing them up to your own liking :)