On 2012-12-17, Andrew Ardill <andrew.ard...@gmail.com> wrote:
> On 17 December 2012 13:30, Woody Wu <narkewo...@gmail.com> wrote:
>> 1. git checkout foo
>> 2. git checkout origin/foo
>> The first method run silently with success, but the second method
>> complains that I got a 'detached HEAD'.  So, I think I don't understand
>> the difference between 'foo' and 'origin/foo'.  Can someone give me a
>> hint?
> Hi Woody,
> I think you are just missing a couple of important distinctions that
> git makes about the different references that exist in your
> repository.
> A remote reference (origin/foo) describes exactly the state of
> somebody else's branch at the time you last synchronised with them. It
> does not make sense for you to be able to 'edit' this state, as it
> doesn't belong to you. Instead, we create a copy of that reference and
> give it a name (git checkout foo origin/foo) and call this a local
> reference (foo). Git then provides machinery around keeping these in
> sync with each other (git branch --set-upstream foo origin/foo) but we
> don't _have_ to keep these in sync at all! In fact, the names can be
> completely arbitrary and we don't have to track the upstream at all.
> If I have some other remote (remote-x) that has the same branch as
> origin but with some other changes I want to look at, we can just
> check that out to another branch (git checkout remote-x-foo
> remote-x/foo), or simply download it as a remote ref and merge the
> changes on top of my existing local branch (git fetch remote-x; git
> checkout foo; git merge remote-x/foo).

Thanks for explaining the concept of branch to me.  Now I understood the
difference between local and remote branch.  But I still have
difficulties in answering my own questions.

1. git checkout foo.
By this command, I think I am checking out files in my local branch
named foo, and after that I also switch to the branch. Right?

2. git checkout origin/foo
By this command, I am checking out files in remote branch origin/foo,
but don't create a local branch, so I am not in any branch now. This is
the reason why git tell me that I am in a 'detached HEAD'. Is this
understanding right?

> There are lots of patterns that can emerge from this functionality,
> but the main thing to remember is that to create changes on top of a
> remote branch, we first need to create a local copy of it. A 'detached
> HEAD' here means that we are looking at the remote repository's branch
> but don't have a local copy of it, so any changes we make might be
> 'lost' (that is, not have an easy to find branch name).

I think here is a little confuse to me.  You mean that a 'detached HEAD'
means I don't have a local copy, but I remember that if I run something
    $ git checkout a-tag-name
then I ususally went into 'detached HEAD' but my local files really get
switched to those files in the tag 'a-tag-name'.  So what does you mean
by 'don't have a local copy'?

Many thanks!

I can't go back to yesterday - because I was a different person then.

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