Rebasing a branch with sub-branches all at once

Question

I often have sub-branches on a branch that I want to rebase onto the mainline. Consider this:

* (Mainline)
*
*
| * (topicA_Branch3)
| *
| *
| * (topicA_Branch2)
| *
| *
| * (topicA_Branch1)
| *
| *
|/
*
*

I want to move all three of these topicA branches onto mainline. Currently, I know two ways to do this:

1. While on topicA_Branch3, execute the command, git rebase Mainline.

   a. At this point, I would have to delete topicA_Branch1 and 2 and manually re-create the branches on the correct commits on the now rebased topicA_Branch3.

2. Another way would be to do three separate commands:

   a. While on topicA_Branch1, do git rebase Mainline.

   b. git rebase --onto topicABranch1 <topicA_Branch1-old-SHA> topicABranch2

   c. git rebase --onto topicABranch2 <topicA_Branch2-old-SHA> topicABranch3

   d. This is kind of cumbersome...

Is there a command that I want that will rebase a branch and bring it's sub-branches with it?

To be clear, I want to end up with this:

* (topicA_Branch3)
*
*
* (topicA_Branch2)
*
*
* (topicA_Branch1)
*
*
* (Mainline)
*
*
*
*

Answer 1

What about that:

 a. While on `topicA_Branch1`, do `git rebase Mainline`.

 b. `git rebase --onto topicABranch1 topicABranch1@{1} topicABranch2`

 c. `git rebase --onto topicABranch2 topicABranch2@{1} topicABranch3` 

 d. ...

This might easily be automated. The syntax topicABranch1@{1} means "the last known state of topicABranch1 before the rebase"