what are different ways between we git diff?

Question

what is the difference between git diff HEAD^ HEAD or git diff HEAD~ HEAD and this git diff HEAD^1 or git diff HEAD~1?

I understand the ones git diff HEAD^ HEAD = git diff HEAD~ HEAD.

and so is git diff HEAD^1 = git diff HEAD~1 ..

are all these diff yielding same output in any case?

Answer 1

I think the main confusion isn't about git diff but about HEAD and HEAD^[num] and HEAD~[num].

EDIT:

HEAD means the current branch you are working at.

And HEAD^[num] means the num'th parent point of a multi-parent node. For a single parent node, [Commit]^[2 or greater] is an invalid expression. ( And git will warn this by fatal: ambiguous argument '1f9a20d^2': unknown revision or path not in the working tree.)

The HEAD~[num] means the num'th ancester commit of a commit node. For a merging node, the ancester is the branch branch you were on when you merged.

Ref this link and this link to read more about HEAD related.

The following picture shows a several way of using Ancestry References in a quite simple situation.

ps. Sincecely apology for previous wrong answer and thanks @torek a lot for correcting it out.

Answer 2

Your examples are not equivalent. If you do not specify a commit to compare against then the diff will contain working tree changes, staged or not.

So, git diff HEAD^ will include working tree changes in the commit, while git diff HEAD^ HEAD will not include working tree changes and will only include the diff between the two commits.

HEAD^, HEAD~, HEAD^1, and HEAD~1 are all identical. They all refer to the first parent of the HEAD commit.

HEAD^^, HEAD~~, and HEAD~2 are identical, they all refer to the first parent of the first parent of the HEAD commit. HEAD^2 is special - it refers the the second parent of the HEAD commit, which is only useful if HEAD is a merge commit.

More information here:

http://git-scm.com/book/ch6-1.html#Ancestry-References