[git] How to pull remote branch from somebody else's repo

I've got a project hosted on GitHub which somebody has forked. On their fork, they've created a new branch "foo" and made some changes. How do I pull their "foo" into a new branch also named "foo" in my repo?

I understand they could submit a pull request to me, but I'd like to initiate this process myself.

Assume the following:

1. Because they forked my project, both our repos share the same 'history'
2. Although GitHub shows their project was forked from mine, my local repository doesn't have any references to this person's project. Do I need to add theirs as a remote?
3. I don't have a branch called "foo" yet - I don't know if I need to manually create this first.
4. I definitely want this pulled into a separate branch and not my master.

If antak's answer:

git fetch [email protected]:<THEIR USERNAME>/<REPO>.git <THEIR BRANCH>:<OUR NAME FOR BRANCH> 

gives you:

Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Then (following Przemek D's advice) use

git fetch https://github.com/<THEIR USERNAME>/<REPO>.git <THEIR BRANCH>:<OUR NAME FOR BRANCH>

GitHub has a new option relative to the preceding answers, just copy/paste the command lines from the PR:

1. Scroll to the bottom of the PR to see the Merge or Squash and merge button
2. Click the link on the right: view command line instructions
3. Press the Copy icon to the right of Step 1
4. Paste the commands in your terminal

The following is a nice expedient solution that works with GitHub for checking out the PR branch from another user's fork. You need to know the pull request ID (which GitHub displays along with the PR title).

Example:

Fixing your insecure code #8
alice wants to merge 1 commit into your_repo:master from her_repo:branch

git checkout -b <branch>
git pull origin pull/8/head

Substitute your remote if different from origin.
Substitute 8 with the correct pull request ID.

No, you don't need to add them as a remote. That would be clumbersome and a pain to do each time.

Grabbing their commits:

git fetch [email protected]:theirusername/reponame.git theirbranch:ournameforbranch

This creates a local branch named ournameforbranch which is exactly the same as what theirbranch was for them. For the question example, the last argument would be foo:foo.

Note :ournameforbranch part can be further left off if thinking up a name that doesn't conflict with one of your own branches is bothersome. In that case, a reference called FETCH_HEAD is available. You can git log FETCH_HEAD to see their commits then do things like cherry-picked to cherry pick their commits.

Pushing it back to them:

Oftentimes, you want to fix something of theirs and push it right back. That's possible too:

git fetch [email protected]:theirusername/reponame.git theirbranch
git checkout FETCH_HEAD

# fix fix fix

git push [email protected]:theirusername/reponame.git HEAD:theirbranch

If working in detached state worries you, by all means create a branch using :ournameforbranch and replace FETCH_HEAD and HEAD above with ournameforbranch.

If the forked repo is protected so you can't push directly into it, and your goal is to make changes to their foo, then you need to get their branch foo into your repo like so:

git remote add protected_repo https://github.com/theirusername/their_repo.git
git fetch protected_repo 
git checkout --no-track protected_repo/foo

Now you have a local copy of foo with no upstream associated to it. You can commit changes to it (or not) and then push your foo to your own remote repo.

git push --set-upstream origin foo

Now foo is in your repo on GitHub and your local foo is tracking it. If they continue to make changes to foo you can fetch theirs and merge into your foo.

git checkout foo 
git fetch protected_repo
git merge protected_repo/foo