difference between git merge origin/master and git pull

Question

fetch, merge, and pull

git fetch and git merge origin/master will fetch & integrate remote changes. Let me explain a common scenario. origin/master is at C. Someone pushed D. You worked on E & F. Note that you will not see D in your local repository until you run git fetch.

   origin/master
    v
A-B-C-E-F < master
     \
     (D) < master on remote

Now you run git fetch. Now you can see D, and origin/master is updated to match the remote repository that it's tracking.

A-B-C-E-F < master
     \
      D < origin/master, master on remote

Now you run git merge, giving you this:

A-B-C-E-F
     \   \
      D---G < master
      ^
    origin/master, master on remote

So now you've integrated your changes on master (E, F) with the new commits on origin/master (D).

git pull is simply a shortcut for the above steps.

git merge without fetching

Running git merge origin/master without the git fetch is pointless. Without a git fetch, your local repository is unaware of any potential changes on the remote repository and origin/master will not have moved. So you're at this state, where D is only on the remote and not present locally:

   origin/master
    v
A-B-C-E-F < master
     \
     (D) < master on remote

Since your local repository does not have D, a git merge origin/master will simply yield:

Already up-to-date.

Because hey, as far as your local repository is concerned, master already has everything in origin/master.

What's best?

None of the above. :)

git fetch
git rebase origin/master master

or a shortcut, git pull -r, but personally I prefer to see the changes before I rebase.
This will replay your changes on master (E, F) on top of origin/master (D) without a yucky merge commit. It yields:

A-B-C-D-E'-F' < master
      ^
   origin/master, master on remote

Note how everything is in a single line, you're ready to push, and the history doesn't look like a friendship bracelet.

One warning - never rebase any commits that have already been pushed. Note that E & F became E' & F' after rebasing. The commits are entirely rewritten, with a new SHA and everything. If you rebase commits that are already public, developers will have their history re-written for them when they pull. And that's awful, and everyone will give you evil eyes and shun you.

git pull is the same as git fetch + git merge

The command

git pull <remote> <branch>

is really just the same as

git fetch <remote>
git merge <remote>/<branch>

So there is no practical difference between

git pull origin master

and

git fetch origin
git merge origin/master

Documentation

As stated in the official Linux Kernel git pull documentation:

In its default mode, git pull is shorthand for git fetch followed by git merge FETCH_HEAD.

More precisely, git pull runs git fetch with the given parameters and calls git merge to merge the retrieved branch heads into the current branch.

Recommended Reading

• Pro Git § 2.5 Git Basics - Working with Remotes - Fetching and Pulling from Your Remotes.

A git pull is going to run a git fetch and then a git merge. If you want to bring your local repository up to speed with a remote repository that is what you would run.

A git fetch is going to import commits from a remote repo without merging them, which gives you the opportunity to review them before integrating.