Git rebase local vs git pull --rebase origin

Question

I have a local (never pushed to a remote) feature branch F1 made from master with a few commits. I don't seem to understand a difference between these two actions (F1 is the current branch):

git fetch origin
git rebase master

and

git pull --rebase origin master

My expectation is that they should be equivalent but they aren't - different results are produced.

What's wrong with my thinking?

Answer 1

1. git fetch origin and git rebase master will apply changes from F1 to local master branch. Assume your commit history looks like below at first (the remote master branch has commit J in remote):

A---B---C---D---E    master
         \
          F---G---H  F1

When you execute git fetch origin and git rebase master, even though origin/master points to J, it will only rebase F1 branch on the top of local master branch (commit E as the graph):

A---B---C---D---E(master)---J origin/master
                 \
                  F---G---H    F1

2. The command git pull --rebase origin master will pull changes from remote master branch at first, then rebase current branch F1 on the top of it:

A---B---C---D---E---J      master,origin/master 
                     \
                      F---G---H  F1

In a word, if local master branch is sync with remote master branch, these two ways have the same result (rebase F1 branch on the top of master branch). If remote master branch has new commit(s) which is(are) not exist on local master branch, the results are different (one rebases on local master branch, the other rebase on origin/master branch).