git-reference/basic/index.html

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layout: reference
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<div class="box">
  <h2>Basic Snapshotting</h2>
  <div class="block">
    <p>
    Git is all about composing and saving snapshots of your project and then
    working with and comparing those snapshots.  This section will explain
    the commands needed to compose and commit snapshots of your project.
    </p>

    <p>
    An important concept here is that Git has an 'index', which acts as sort
    of a staging area for your snapshot.  This allows you to build up a series
    of well composed snapshots from changed files in your working directory, 
    rather than having to commit all of the file changes at once.
    </p>

    <p class="nutshell">
    <strong>In a nutshell</strong>, you will use <code>git add</code> to start tracking new
    files and also to stage changes to already tracked files, then 
    <code>git status</code> and <code>git diff</code> to see what has been
    modified and staged and finally <code>git commit</code> to record your
    snapshot into your history.  This will be the basic workflow that you use
    most of the time.
    </p>

  </div>
</div>

<div class="box">
  <h2>
    <span class="docs">
      <a href="#">docs</a> &nbsp;
      <a href="#">book</a>
    </span>
    <a name="add">git add</a>
    <span class="desc">adds file contents to the staging area</span>
  </h2>

  <div class="block">
    <p>
    In Git, you have to add file contents to your staging area before you 
    can commit them.  If the file is new, you can run <code>git add</code>
    to initially add the file to your staging area, but even if the file
    is already "tracked" - ie, it was in your last commit - you still need
    to call <code>git add</code> to add new modifications to your staging
    area. Let's see a few examples of this.
    </p>

    <p>Going back to our Hello World example, once we've initiated the project,
    we would now start adding our files to it and we would do that with 
    <code>git add</code>.  We can use <code>git status</code> to see what the
    state of our project is.
    </p>

<pre>
$ git status -s
?? README
?? hello.rb
</pre>

    So right now we have two untracked files.  We can now add them.

<pre>
$ git add README hello.rb
</pre>
    
    Now if we run <code>git status</code> again, we'll see that they've been
    added.

<pre>
$ git status -s
A  README
A  hello.rb
</pre>

    <p>OK, so now if we edit one of these files and run <code>git status</code>
    again, we will see something odd.</p>
<pre>
$ vim README
$ git status -s
AM README
A  hello.rb
</pre>

    <p>The 'AM' status means that the file has been modified on disk since we
    last added it.  This means that if we commit our snapshot right now, we will
    be recording the version of the file when we last ran <code>git add</code>,
    not the version that is on our disk.  Git does not assume that what the file
    looks like on disk is neccesarily what you want to snapshot - you have to
    tell Git with the <code>git add</code> command.
    </p>

    <p class="nutshell">
    <strong>In a nutshell</strong>, 
    you run <code>git add</code> on a file when you want to 
    include whatever changes you've made to it in your next commit snapshot.
    Anything you've changed that is not added will not be included - this means
    you can craft your snapshots with a bit more precision than most other SCM
    systems.</p>

    <p>For a very interesting example of using this flexibility to stage only
    parts of modified files at a time, see the '-p' option to 
    <code>git add</code> in the Pro Git book.</p>


  </div>

</div>

<div class="box">
  <h2>
    <span class="docs">
      <a href="#">docs</a> &nbsp;
      <a href="#">book</a>
    </span>
    <a name="status">git status</a>
    <span class="desc">view the status of your files in the working directory and staging area</span>
  </h2>

  <div class="block">
    <p>As you saw in the <code>git add</code> section, in order to see what the
    status of your staging area is compared to the code in your working 
    directory, you can run the <code>git status</code> command. I demonstrated
    using it with the <code>-s</code> option, which gives you short output.
    Without that flag, the <code>git status</code> command will give you more
    context and hints.  Here is the same status output with and without the 
    <code>-s</code>.  The short output looks like this:
    </p>

<pre>
<b>$ git status -s</b>
<span class="green">A</span><span class="red">M</span> README
<span class="green">A</span>  hello.rb
</pre>

    Where the same status with the long output looks like this:

<pre>
<b>$ git status</b>
# On branch master
#
# Initial commit
#
# Changes to be committed:
#   (use "git rm --cached <file>..." to unstage)
#
# <span class="green">new file:   README</span>
# <span class="green">new file:   hello.rb</span>
#
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
# <span class="red">modified:   README</span>
#
</pre>

    <p>You can easily see how much more compact the short output is, but the
    long output has useful tips and hints as to what commands you may want to 
    use next.
    </p>

    <p>Git will also tell you about files that were deleted since your last 
    commit or files that were modified or staged since your last commit.</p>

<pre>
<b>$ git status -s</b>
<span class="green">M</span>  README
 <span class="red">D</span> hello.rb
</pre>

    You can see there are two columns in the short status output.  The first
    column is for the staging area, the second is for the working directory.
    So for example, if you have the README file staged and then you modify
    it again without running <code>git add</code> a second time, you'll see 
    this:

<pre>
<b>$ git status -s</b>
<span class="green">M</span><span class="red">M</span> README
 <span class="red">D</span> hello.rb
</pre>
    <p class="nutshell">
    <strong>In a nutshell</strong>, 
    you run <code>git status</code> to see if anything has been modified 
    and/or staged since your last commit so you can decide if you want to
    commit a new snapshot and what will be recorded in it.
    </p>


    </p>

  </div>
</div>

<p><a href="/basic">On to Branching and Merging &#187;</a></p>