344 lines
15 KiB
HTML
344 lines
15 KiB
HTML
---
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layout: reference
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---
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<div class="box">
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<h2>
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<span class="docs">
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<a target="new" href="http://progit.org/book/ch2-5.html">book</a>
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</span>
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Sharing and Updating Projects
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</h2>
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<div class="block">
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<p>
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Git doesn't have a central server like Subversion. All of the commands
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so far have been done locally, just updating a local database.
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To collaborate with other developers in Git, you have to put all that
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data on a server that the other developers have access to. The way Git
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does this is to synchronize your data with another repository. There
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is no real difference between a server and a client - a Git repository
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is a Git repository and you can synchronize between any two easily.
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</p>
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<p>Once you have a Git repository, either one that you set up on your
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own server, or one hosted someplace like GitHub, you can tell Git to
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either push any data that you have that is not in the remote repository
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up, or you can ask Git to fetch differences down from the other repo.
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</p>
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<p>You can do this any time you are online, it does not have to correspond
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with a <code>commit</code> or anything else. Generally you will do a
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number of commits locally, then fetch data from the online shared repository
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you cloned the project from to get up to date, merge any new work into the
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stuff you did, then push your changes back up.</p>
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<p class="nutshell">
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<b>In a nutshell</b> you can update your project with <code>git fetch</code>
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and share your changes with <code>git push</code>. You can manage your
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remote repositories with <code>git remote</code>.
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</p>
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</div>
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</div>
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<div class="box">
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<h2>
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<span class="docs">
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<a target="new" href="http://www.kernel.org/pub/software/scm/git/docs/git-remote.html">docs</a>
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<a target="new" href="http://progit.org/book/ch2-5.html#showing_your_remotes">book</a>
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</span>
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<a name="remote">git remote</a>
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<span class="desc">list, add and delete remote repository aliases</span>
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</h2>
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<div class="block">
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<p>Unlike centralized version control systems that have a client that is
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very different from a server, Git repositories are all basically equal and
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you simply synchronize between them. This makes it easy to have more than
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one remote repository - you can have some that you have read-only access to
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and others that you can write to as well.</p>
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<p>So that you don't have to use the full URL of a remote repository every
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time you want to synchronize with it, Git stores an alias or nickname for
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each remote repository URL you are interested in. You use the
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<code>git remote</code> command to manage this list of remote repos that
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you care about.</p>
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<h4>
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git remote
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<small>list your remote aliases</small>
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</h4>
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<p>Without any arguments, Git will simply show you the remote repository
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aliases that it has stored. By default, if you cloned the project (as
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opposed to creating a new one locally), Git will automatically add the
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URL of the repository that you cloned from under the name 'origin'. If
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you run the command with the <code>-v</code> option, you can see the
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actual URL for each alias.</p>
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<pre>
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<b>$ git remote</b>
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origin
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<b>$ git remote -v</b>
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origin git@github.com:schacon/git-reference.git (fetch)
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origin git@github.com:schacon/git-reference.git (push)
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</pre>
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<p>You see the URL there twice because Git allows you to have different
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push and fetch URLs for each remote in case you want to use different
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protocols for reads and writes.</p>
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<h4>
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git remote add
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<small>add a new remote repository of your project</small>
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</h4>
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<p>If you want to share a locally created repository, or you want to take
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contributions from someone elses repository - if you want to interact in
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any way with a new repository, it's generally easiest to add it as a remote.
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You do that by running <code>git remote add [alias] [url]</code>. That
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adds <code>[url]</code> under a local remote named <code>[alias]</code>.</p>
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<p>For example, if we want to share our Hello World program with the world,
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we can create a new repository on a server (I'll use GitHub as an example),
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which should give you a URL, in this case "git@github.com:schacon/hw.git".
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To add that to our project so we can push to it and fetch updates from it
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we would do this:</p>
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<pre>
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<b>$ git remote</b>
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<b>$ git remote add github git@github.com:schacon/hw.git</b>
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<b>$ git remote -v</b>
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github git@github.com:schacon/hw.git (fetch)
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github git@github.com:schacon/hw.git (push)
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</pre>
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<p>Like the branch naming, remote alias names are arbitrary - just as 'master'
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has no special meaning but is widely used because <code>git init</code>
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sets it up by default, 'origin' is often used as a remote name because
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<code>git clone</code> sets it up by default as the cloned-from URL. In
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this case I've decided to name my remote 'github', but I could have really
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named it just about anything.
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</p>
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<h4>
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git remote rm
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<small>removing an existing remote alias</small>
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</h4>
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<p>Git addeth and Git taketh away. If you need to remove a remote - you are
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not using it anymore, the project is gone, etc - you can remove it with
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<code>git remote rm [alias]</code>.</p>
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<pre>
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<b>$ git remote -v</b>
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github git@github.com:schacon/hw.git (fetch)
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github git@github.com:schacon/hw.git (push)
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<b>$ git remote add origin git://github.com/pjhyett/hw.git</b>
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<b>$ git remote -v</b>
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github git@github.com:schacon/hw.git (fetch)
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github git@github.com:schacon/hw.git (push)
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origin git://github.com/pjhyett/hw.git (fetch)
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origin git://github.com/pjhyett/hw.git (push)
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<b>$ git remote rm origin</b>
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<b>$ git remote -v</b>
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github git@github.com:schacon/hw.git (fetch)
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github git@github.com:schacon/hw.git (push)
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</pre>
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<p class="nutshell">
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<b>In a nutshell</b> with <code>git remote</code> you can list our
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remote repositories and whatever URL
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that repository is using. You can use <code>git remote add</code> to
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add new remotes and <code>git remote rm</code> to delete existing ones.
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</p>
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</div>
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</div>
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<div class="box">
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<h2>
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<span class="docs">
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<a target="new" href="http://www.kernel.org/pub/software/scm/git/docs/git-fetch.html">docs</a>
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<a target="new" href="http://progit.org/book/ch2-5.html#fetching_and_pulling_from_your_remotes">book</a>
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</span>
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<a name="fetch">git fetch</a>
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<span class="desc">download new branches and data from a remote repository</span>
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</h2>
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<br/>
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<h2>
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<span class="docs">
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<a target="new" href="http://www.kernel.org/pub/software/scm/git/docs/git-pull.html">docs</a>
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<a target="new" href="http://progit.org/book/">book</a>
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</span>
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<a name="pull">git pull</a>
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<span class="desc">fetch from a remote repo and try to merge into the current branch</span>
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</h2>
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<div class="block">
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<p>Git has two commands to update itself from a remote repository.
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<code>git fetch</code> will synchronize you with another repo, pulling down any data
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that you do not have locally and giving you bookmarks to where each branch on
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that remote was when you synchronized. These are called "remote branches" and are
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identical to local branches except that Git will not allow you to check them out -
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however, you can merge from them, diff them to other branches, run history logs on
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them, etc. You do all of that stuff locally after you synchronize.
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</p>
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<p>The second command that will fetch down new data from a remote server is
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<code>git pull</code>. This command will basically run a <code>git fetch</code>
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immediately followed by a <code>git merge</code> of the branch on that remote
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that is tracked by whatever branch you are currently in. I personally don't much
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like this command - I prefer running <code>fetch</code> and <code>merge</code>
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separately. Less magic, less problems. However, if you like this idea, you
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can read about it in more detail in the
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<a target="new" href="http://www.kernel.org/pub/software/scm/git/docs/git-pull.html">official docs</a>.
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</p>
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<p>Assuming you have a remote all set up and you want to pull in updates, you
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would first run <code>git fetch [alias]</code> to tell Git to fetch down all the
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data it has that you do not, then you would run <code>git merge [alias]/[branch]</code>
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to merge into your current branch anything new you see on the server
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(like if someone else has pushed in the meantime). So, if I were working on my
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Hello World project with several other people and I wanted to bring in any changes
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that had been pushed since I last connected, I would do something like this:</p>
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<pre>
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<b>$ git fetch github</b>
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remote: Counting objects: 4006, done.
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remote: Compressing objects: 100% (1322/1322), done.
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remote: Total 2783 (delta 1526), reused 2587 (delta 1387)
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Receiving objects: 100% (2783/2783), 1.23 MiB | 10 KiB/s, done.
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Resolving deltas: 100% (1526/1526), completed with 387 local objects.
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From github.com:schacon/hw
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8e29b09..c7c5a10 master -> github/master
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0709fdc..d4ccf73 c-langs -> github/c-langs
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6684f82..ae06d2b java -> github/java
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* [new branch] ada -> github/ada
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* [new branch] lisp -> github/lisp
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</pre>
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<p>I can see that since the last time I synchronized with this remote, five branches
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have been added or updated. The 'ada' and 'lisp' branches are new, where the
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'master', 'c-langs' and 'java' branches have been updated. In this case, my team
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is pushing proposed updates to remote branches for review before they're merged
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into 'master'.
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</p>
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<p>You can see the mapping that Git makes. The 'master' branch on the remote
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repository becomes a branch named 'github/master' locally. That way now I can
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merge the 'master' branch on that remote into my local 'master' branch by running
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<code>git merge github/master</code>. Or, I can see what new commits are on that
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branch by running <code>git log github/master ^master</code>. If your remote
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is named 'origin' it would be <code>origin/master</code> instead. Almost any
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command you would run using local branches you can use remote branches with too.
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</p>
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<p>If you have more than one remote repository, you can either fetch from specific
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ones by running <code>git fetch [alias]</code> or you can tell Git to synchronize
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with all of your remotes by running <code>git fetch --all</code>.
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<p class="nutshell">
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<b>In a nutshell</b> you run <code>git fetch [alias]</code> to synchronize your
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repository with a remote repository, fetching all the data it has that you do
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not into branch references locally for merging and whatnot.
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</p>
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</div>
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</div>
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<div class="box">
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<h2>
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<span class="docs">
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<a target="new" href="http://www.kernel.org/pub/software/scm/git/docs/git-push.html">docs</a>
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<a target="new" href="http://progit.org/book/ch2-5.html#pushing_to_your_remotes">book</a>
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</span>
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<a name="push">git push</a>
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<span class="desc">push your new branches and data to a remote repository</span>
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</h2>
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<div class="block">
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<p>To share the cool commits you've done with others, you need to push your
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changes to the remote repository. To do this, you run
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<code>git push [alias] [branch]</code> which will attempt to make your [branch]
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the new [branch] on the [alias] remote. Let's try it by initially pushing
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our 'master' branch to the new 'github' remote we created earlier.</p>
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<pre>
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<b>$ git push github master</b>
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Counting objects: 25, done.
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Delta compression using up to 2 threads.
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Compressing objects: 100% (25/25), done.
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Writing objects: 100% (25/25), 2.43 KiB, done.
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Total 25 (delta 4), reused 0 (delta 0)
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To git@github.com:schacon/hw.git
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* [new branch] master -> master
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</pre>
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<p>Pretty easy. Now if someone clones that repository they will get exactly
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what I have committed and all of its history.</p>
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<p>What if I have a topic branch like the 'erlang' branch we created earlier
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and I just want to share that? You can just push that branch instead.
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<pre>
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<b>$ git push github erlang</b>
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Counting objects: 7, done.
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Delta compression using up to 2 threads.
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Compressing objects: 100% (6/6), done.
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Writing objects: 100% (6/6), 652 bytes, done.
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Total 6 (delta 1), reused 0 (delta 0)
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To git@github.com:schacon/hw.git
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* [new branch] erlang -> erlang
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</pre>
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<p>Now when people clone or fetch from that repository, they'll get an 'erlang'
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branch they can look at and merge from. You can push any branch to any
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remote repository that you have write access to in this way. If your branch
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is already on the server, it will try to update it, if it is not, Git will
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add it.</p>
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<p>The last major issue you run into with pushing to remote branches is the
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case of someone pushing in the meantime. If you and another developer clone
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at the same time, you both do commits, then she pushes and then you try to
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push, Git will by default not allow you to overwrite her changes. Instead,
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it basically runs <code>git log</code> on the branch you're trying to push and
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makes sure it can see the current tip of the server's branch in your push's
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history. If it can't see what is on the server in your history, it concludes
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that you are out of date and will reject your push. You will rightly have to
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fetch, merge then push again - which makes sure you take her changes into
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account.</p>
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<p>This is what happens when you try to push a branch to a remote branch
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that has been updated in the meantime:</p>
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<pre>
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<b>$ git push github master</b>
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To git@github.com:schacon/hw.git
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! [rejected] master -> master (non-fast-forward)
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error: failed to push some refs to 'git@github.com:schacon/hw.git'
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To prevent you from losing history, non-fast-forward updates were rejected
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Merge the remote changes before pushing again. See the 'Note about
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fast-forwards' section of 'git push --help' for details.
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</pre>
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<p>You can fix this by running <code>git fetch github; git merge github/master</code>
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and then pushing again.
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<p class="nutshell">
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<b>In a nutshell</b> you run <code>git push [alias] [branch]</code> to update a
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remote repository with the changes you've made locally. It will take what your
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[branch] looks like and push it to be [branch] on the remote, if possible. If
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someone else has pushed since you last fetched and merged, the Git server will
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deny your push until you are up to date.
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</p>
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</div>
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</div>
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<p><a href="/inspect">On to Inspection and Comparison »</a></p>
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