Git doesn't have a central server like Subversion. All of the commands so far have been done locally, just updating a local database. To collaborate with other developers in Git, you have to put all that data on a server that the other developers have access to. The way Git does this is to syncronize your data with another repository. There is no real difference between a server and a client - a Git repository is a Git repository and you can syncronize between any two easily.
Once you have a Git repository, either one that you set up on your own server, or one hosted someplace like GitHub, you can tell Git to either push any data that you have that is not in the remote repository up, or you can ask Git to fetch differences down from the other repo.
You can do this any time you are online, it does not have to correspond
with a commit or anything else. Generally you will do a
number of commits locally, then fetch data from the online shared repository
you cloned the project from to get up to date, merge any new work into the
stuff you did, then push your changes back up.
In a nutshell you can update your project with git fetch
and share your changes with git push. You can manage your
remote repositories with git remote.
Unline centralized version control systems that have a client that is very different from a server, Git repositories are all basically equal and you simply syncronize between them. This makes it easy to have more than one remote repository - you can have some that you have read-only access to and others that you can write to as well.
So that you don't have to use the full URL of a remote repository every
time you want to syncronize with it, Git stores an alias or nickname for
each remote repository URL you are interested in. You use the
git remote command to manage this list of remote repos that
you care about.
Without any arguments, Git will simply show you the remote repository
aliases that it has stored. By default, if you cloned the project (as
opposed to creating a new one locally), Git will automatically add the
URL of the repository that you cloned from under the name 'origin'. If
you run the command with the -v option, you can see the
actual URL for each alias.
$ git remote origin $ git remote -v origin git@github.com:schacon/git-reference.git (fetch) origin git@github.com:schacon/git-reference.git (push)
You see the URL there twice because Git allows you to have different push and fetch URLs for each remote in case you want to use different protocols for reads and writes.
If you want to share a locally created repository, or you want to take
contributions from someone elses repository - if you want to interact in
any way with a new repository, it's generally easiest to add it as a remote.
You do that by running git remote add [alias] [url]. That
adds [url] under a local remote named [alias].
For example, if we want to share our Hello World program with the world, we can create a new repository on a server (I'll use GitHub as an example), which should give you a URL, in this case "git@github.com:schacon/hw.git". To add that to our project so we can push to it and fetch updates from it we would do this:
$ git remote $ git remote add github git@github.com:schacon/hw.git $ git remote -v github git@github.com:schacon/hw.git (fetch) github git@github.com:schacon/hw.git (push)
Like the branch naming, remote alias names are arbitrary - just as 'master'
has no special meaning but is widely used because git init
sets it up by default, 'origin' is often used as a remote name because
git clone sets it up by default as the cloned-from URL. In
this case I've decided to name my remote 'github', but I could have really
named it just about anything.
Git addeth and Git taketh away. If you need to remove a remote - you are
not using it anymore, the project is gone, etc - you can remove it with
git remote rm [alias].
$ git remote -v github git@github.com:schacon/hw.git (fetch) github git@github.com:schacon/hw.git (push) $ git remote add origin git://github.com/pjhyett/hw.git $ git remote -v github git@github.com:schacon/hw.git (fetch) github git@github.com:schacon/hw.git (push) origin git://github.com/pjhyett/hw.git (fetch) origin git://github.com/pjhyett/hw.git (push) $ git remote rm origin $ git remote -v github git@github.com:schacon/hw.git (fetch) github git@github.com:schacon/hw.git (push)
In a nutshell with git remote you can list our
remote repositories and whatever URL
that repository is using. You can use git remote add to
add new remotes and git remote rm to delete existing ones.
Git has two commands to update itself from a remote repository.
git fetch will syncronize you with another repo, pulling down any data
that you do not have locally and giving you bookmarks to where each branch on
that remote was when you syncronized. These are called "remote branches" and are
identical to local branches except that Git will not allow you to check them out -
however, you can merge from them, diff them to other branches, run history logs on
them, etc. You do all of that stuff locally after you syncronize.
The second command that will fetch down new data from a remote server is
git pull. This command will basically run a git fetch
immediately follwed by a git merge of the branch on that remote
that is tracked by whatever branch you are currently in. I personally don't much
like this command - I prefer running fetch and merge
seperately. Less magic, less problems. However, if you like this idea, you
can read about it in more detail in the.
official docs.
Assuming you have a remote all set up and you want to pull in updates, you
would first run git fetch [alias] to tell Git to fetch down all the
data it has that you do not, then you would run git merge [alias]/[branch]
to merge into your current branch anything new you see on the server
(like if someone else has pushed in the meantime). So, if I were working on my
Hello World project with several other people and I wanted to bring in any changes
that had been pushed since I last connected, I would do something like this:
$ git fetch github remote: Counting objects: 4006, done. remote: Compressing objects: 100% (1322/1322), done. remote: Total 2783 (delta 1526), reused 2587 (delta 1387) Receiving objects: 100% (2783/2783), 1.23 MiB | 10 KiB/s, done. Resolving deltas: 100% (1526/1526), completed with 387 local objects. From github.com:schacon/hw 8e29b09..c7c5a10 master -> github/master 0709fdc..d4ccf73 c-langs -> github/c-langs 6684f82..ae06d2b java -> github/java * [new branch] ada -> github/ada * [new branch] lisp -> github/lisp
I can see that since the last time I synchronized with this remote, five branches have been added or updated. The 'ada' and 'lisp' branches are new, where the 'master', 'c-langs' and 'java' branches have been updated. In this case, my team is pushing proposed updates to remote branches for review before they're merged into 'master'.
You can see the mapping that Git makes. The 'master' branch on the remote
repository becomes a branch named 'github/master' locally. That way now I can
merge the 'master' branch on that remote into my local 'master' branch by running
git merge github/master. Or, I can see what new commits are on that
branch by running git log github/master ^master. If your remote
is named 'origin' it would be origin/master instead. Almost any
command you would run using local branches you can use remote branches with too.
If you have more than one remote repository, you can either fetch from specific
ones by running git fetch [alias] or you can tell Git to syncronize
with all of your remotes by running git fetch --all.
In a nutshell you run git fetch [alias] to syncronize your
repository with a remote repository, fetching all the data it has that you do
not into branch references locally for merging and whatnot.