Has the Pro Git book got the syntax of git-rebase backwards?

Question

Just as the title illustrates. I recently tried to run a git rebase command that had the reverse effect from what the Git pro's section on rebasing had. Maybe I interpreted it wrong, but its driving me crazy because what I thought was supposed to happen failed and I need to know what went wrong.

The section that I refer to is under More Interesting Rebases, particularly with the example when you rebase the server work branch onto the master branch. Git Rebasing.

The way how I interpreted was that the server work would be pasted on top of the master work, which is clearly what it happening based on the illustration.

I had two branches named OTWO-3196 (Capistrano configurations) and origin/orgs_phase_2 on my local machine. What I intended to do was to have the origin/orgs_phase_2 work rebase on top of my OTWO-3196 (Capistrano configurations) work. I typed into the terminal this command:

git rebase OTWO-3196(basebranch) origin/orgs_phase_2(topicbranch)

What I thought would place the orgs_phase_2 work on OTWO-3196 (Capistrano work) instead placed the OTWO-3196 (Capistrano work) onto orgs_phase_2. This was the exact reverse of what I wanted.

This command however worked:

git rebase origin/orgs_phase_2 OTWO-3196

This placed the work of origin/orgs_phase_2 onto OTWO-3196.

Did I interpret the command wrong? Is the book incorrect? What exactly happened? An extra pair of eyes would be helpful. Thanks.

Answer 1

I don't know what you did, or think you did, but origin/orgs_phase_2 is a remote-tracking branch. Its only purpose is to indicate where the branch reference called orgs_phase_2 pointed to in the remote repo called origin the last time you communicated with the latter. The only way such a reference can move is via a fetch or a push. In particular, you can't rebase a remote-tracking branch.

Besides, the Pro Git book is correct. You have got the git-rebase syntax backwards. Git's rebase works as advertised in that book,

git rebase [basebranch] [topicbranch]

checks out the topic branch [...] for you and replays it onto the base branch [...]

and in the git-rebase man page,

Assume the following history exists and the current branch is "topic":

      A---B---C topic
     /
D---E---F---G master

From this point, the result of either of the following commands:

git rebase master
git rebase master topic

would be:

              A'--B'--C' topic
             /
D---E---F---G master

---

To fix ideas, here is a baby example that you can reproduce at home:

#!/bin/bash

# set things up
cd ~/Desktop
mkdir test
cd test
git init

# write an initial shopping list
printf "4 pears\n" > shopping.txt
printf "3 lemons\n" >> shopping.txt 
printf "1 stalk of celery\n" >> shopping.txt 
printf "4 bananas\n" >> shopping.txt 

# make a first commit on master
git add shopping.txt
git commit -m "add shopping list"

# modify the shopping list and make a second commit on master
sed -i '' 's/4 pears/4 apples/' shopping.txt 
git add shopping.txt
git commit -m "replace pears by apples"

# create and check out a new branch called "kidscominghome"
git checkout -b kidscominghome

# make two more commits on kidscominghome
printf "16 pots of yoghurt\n" >> shopping.txt
git add shopping.txt
git commit -m "add yoghurt"
printf "beer\n" >> shopping.txt 
git add shopping.txt
git commit -m "add beer"

# check out master, modify the file, and make one more commit
git checkout master
sed -i '' 's/stalk of celery/cauliflower/' shopping.txt 
git add shopping.txt
git commit -m "replace celery by cauliflower"

At this stage, the output of

git log --graph --decorate --oneline --all

should be

* 5a0e340 (HEAD, master) replace celery by cauliflower
| * d3d22d0 (kidscominghome) add beer
| * edd730d add yoghurt
|/  
* 7dc55b7 replace pears by apples
* 7079948 add shopping list

Here is a nicer-looking graph showing the same history:

Now, if you run

git rebase master kidscominghome

and then run the same git log command, you should see

* 2acf37d (HEAD, kidscominghome) add beer
* dfac4a8 add yoghurt
* 5a0e340 (master) replace celery by cauliflower
* 7dc55b7 replace pears by apples
* 7079948 add shopping list

Again, here is a nicer-looking graph showing the same history:

As advertised, the kidscominghome branch has been checked out, and the commits that were only reachable from kidcominghome have been replayed on top of master; not the other way around!