Asked  6 Months ago    Answers:  5   Viewed   38 times

I work on a project that has 2 branches, A and B. I typically work on branch A, and merge stuff from branch B. For the merging, I would typically do:

git merge origin/branchB

However, I would also like to keep a local copy of branch B, as I may occasionally check out the branch without first merging with my branch A. For this, I would do:

git checkout branchB
git pull
git checkout branchA

Is there a way to do the above in one command, and without having to switch branch back and forth? Should I be using git update-ref for that? How?



The Short Answer

As long as you're doing a fast-forward merge, then you can simply use

git fetch <remote> <sourceBranch>:<destinationBranch>


# Merge local branch foo into local branch master,
# without having to checkout master first.
# Here `.` means to use the local repository as the "remote":
git fetch . foo:master

# Merge remote branch origin/foo into local branch foo,
# without having to checkout foo first:
git fetch origin foo:foo

While Amber's answer will also work in fast-forward cases, using git fetch in this way instead is a little safer than just force-moving the branch reference, since git fetch will automatically prevent accidental non-fast-forwards as long as you don't use + in the refspec.

The Long Answer

You cannot merge a branch B into branch A without checking out A first if it would result in a non-fast-forward merge. This is because a working copy is needed to resolve any potential conflicts.

However, in the case of fast-forward merges, this is possible, because such merges can never result in conflicts, by definition. To do this without checking out a branch first, you can use git fetch with a refspec.

Here's an example of updating master (disallowing non-fast-forward changes) if you have another branch feature checked out:

git fetch upstream master:master

This use-case is so common, that you'll probably want to make an alias for it in your git configuration file, like this one:

    sync = !sh -c 'git checkout --quiet HEAD; git fetch upstream master:master; git checkout --quiet -'

What this alias does is the following:

  1. git checkout HEAD: this puts your working copy into a detached-head state. This is useful if you want to update master while you happen to have it checked-out. I think it was necessary to do with because otherwise the branch reference for master won't move, but I don't remember if that's really right off-the-top of my head.

  2. git fetch upstream master:master: this fast-forwards your local master to the same place as upstream/master.

  3. git checkout - checks out your previously checked-out branch (that's what the - does in this case).

The syntax of git fetch for (non-)fast-forward merges

If you want the fetch command to fail if the update is non-fast-forward, then you simply use a refspec of the form

git fetch <remote> <remoteBranch>:<localBranch>

If you want to allow non-fast-forward updates, then you add a + to the front of the refspec:

git fetch <remote> +<remoteBranch>:<localBranch>

Note that you can pass your local repo as the "remote" parameter using .:

git fetch . <sourceBranch>:<destinationBranch>

The Documentation

From the git fetch documentation that explains this syntax (emphasis mine):


The format of a <refspec> parameter is an optional plus +, followed by the source ref <src>, followed by a colon :, followed by the destination ref <dst>.

The remote ref that matches <src> is fetched, and if <dst> is not empty string, the local ref that matches it is fast-forwarded using <src>. If the optional plus + is used, the local ref is updated even if it does not result in a fast-forward update.

See Also

  1. Git checkout and merge without touching working tree

  2. Merging without changing the working directory

Tuesday, June 1, 2021
answered 6 Months ago

You have to add the original repository (the one you forked) as a remote.

From the GitHub documentation on forking a repository:

Screenshot of the old GitHub interface with a rectangular lens around the "Fork" button

Once the clone is complete your repo will have a remote named “origin” that points to your fork on GitHub.
Don’t let the name confuse you, this does not point to the original repo you forked from. To help you keep track of that repo we will add another remote named “upstream”:

$ git remote add upstream
$ git fetch upstream

# then: (like "git pull" which is fetch + merge)
$ git merge upstream/master master

# or, better, replay your local work on top of the fetched branch
# like a "git pull --rebase"
$ git rebase upstream/master

There's also a command-line tool (hub) which can facilitate the operations above.

Here's a visual of how it works:

Flowchart on the result after the commands are executed

See also "Are Git forks actually Git clones?".

Tuesday, June 1, 2021
answered 6 Months ago

It seems like you want the files ignored but they have already been commited. .gitignore has no effect on files that are already in the repo so they need to be removed with git rm --cached. The --cached will prevent it from having any effect on your working copy and it will just mark as removed the next time you commit. After the files are removed from the repo then the .gitignore will prevent them from being added again.

But you have another problem with your .gitignore, you are excessively using wildcards and its causing it to match less than you expect it to. Instead lets change the .gitignore and try this.

Sunday, June 6, 2021
answered 6 Months ago

Your refs are getting packed for performance reasons they can now be found in .git/packed-refs cat .git/packed-refs. This man page does a pretty good job of explaining it

Saturday, July 31, 2021
answered 4 Months ago

There are two excellent Stack Overflow responses which address this problem:

How do I tell git to always select my local version for conflicted merges on a specific file?


.gitattributes & individual merge strategy for a file

I'd suggest reading through the top answer in the first link. It's long, but very detailed and informative.

Saturday, October 9, 2021
answered 2 Months ago
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