What's the difference between HEAD^ and HEAD~ in Git?

Question

When I specify an ancestor commit object in Git, I\'m confused between HEAD^ and HEAD~.

Both have a \"numbered\" version like HEAD^3<

Answer 1

Simplistically:

• ~ specifies ancestors
• ^ specifies parents

You can specify one or more branches when merging. Then a commit has two or more parents and then ^ is useful to indicate parents.

Suppose you are on branch A and you have two more branches: B and C.

On each branch the three last commits are:

• A: A1, A2, A3
• B: B1, B2, B3
• C: C1, C3, C3

If now on branch A you execute the command:

git merge B C

then you are combining three branches together (here your merge commit has three parents)

and

~ indicates the n'th ancestor in the first branch, so

• HEAD~ indicates A3
• HEAD~2 indicates A2
• HEAD~3 indicates A1

^ indicates the n'th parent, so

• HEAD^ indicates A3
• HEAD^2 indicates B3
• HEAD^3 indicates C3

The next use of ~ or ^ next to each other is in the context of the commit designated by previous characters.

Notice 1:

• HEAD~3 is always equal to: HEAD~~~ and to: HEAD^^^ (every indicates A1),

        and generally:

• HEAD~n is always equal to: HEAD~...~ (n times ~) and to: HEAD^...^ (n times ^).

Notice 2:

• HEAD^3 is not the same as HEAD^^^ (the first indicates C3 and the second indicates A1),

        and generally:

• HEAD^1 is the same as HEAD^,
• but for n > 1: HEAD^n is always not the same as HEAD^...^ (n times ~).