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<h1><a href="http://wbowam.github.io/git-fu-xi-gong-gu-2.html"> git 复习巩固(2) </a></h1>
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<h4 id="1">1. 对象名<a class="headerlink" href="#1" title="Permanent link">¶</a></h4>
<p><code>6ff87c4664981e4397625791c8ea3bbb5f2279a3</code> <br />
<em> 所有用来表示项目历史信息的文件,是通过一个40个字符的（40-digit）“对象名”来索引的.<br />
</em> 每一个“对象名”都是对“对象”内容做SHA1哈希计算得来的，（SHA1是一种密码学的哈希算法）。这样就意味着两个不同内容的对象不可能有相同的“对象名”。</p>
<h4 id="2">2. 对象<a class="headerlink" href="#2" title="Permanent link">¶</a></h4>
<ul>
<li>有四种类型的对象："blob"、"tree"、 "commit" 和"tag" </li>
</ul>
<h4 id="3-blob">3. Blob 对象<a class="headerlink" href="#3-blob" title="Permanent link">¶</a></h4>
<p>新文件纳入到 Git 后会被五马分尸，它的内容被扔到在一个 blob 对象中，它的对象名是基于内容运算生成的一个 40个字符的 SHA1值。</p>
<p>blob 没有文件名，只有内容。 </p>
<p><img alt="blob" src="http://mednoter.com/media/files/2014/jul/29-object-blob.png" /></p>
<h4 id="4-tree">4. Tree 对象<a class="headerlink" href="#4-tree" title="Permanent link">¶</a></h4>
<p>一个 tree 对象就是一大坨指针，指向：</p>
<ul>
<li>其他 small tree（子级 tree）</li>
<li>blob
可以把 Tree 对象想象为 Linux 文件系统中的目录，记录了子目录的信息、文件信息。 </li>
</ul>
<p><img alt="tree" src="http://mednoter.com/media/files/2014/jul/29-object-tree.png" /></p>
<h4 id="5-commit">5. Commit 对象<a class="headerlink" href="#5-commit" title="Permanent link">¶</a></h4>
<p>一个 commit 对象由以下几部分组成</p>
<ul>
<li>作者</li>
<li>提交者</li>
<li>注释</li>
<li>指向一个 big tree 的指针 </li>
</ul>
<p><img alt="commit" src="http://mednoter.com/media/files/2014/jul/29-object-commit.png" /></p>
<h3 id="6-3blob-tree-commit">6. 我们已经了解了3种主要对象类型(blob, tree 和 commit), 让我们大概了解一下它们怎么组合到一起的<a class="headerlink" href="#6-3blob-tree-commit" title="Permanent link">¶</a></h3>
<p>如果我们一个小项目, 有如下的目录结构:</p>
<div class="highlight"><pre><span class="err">$</span><span class="o">></span><span class="n">tree</span>
<span class="p">.</span>
<span class="o">|--</span> <span class="n">README</span>
<span class="err">`</span><span class="o">--</span> <span class="n">lib</span>
<span class="o">|--</span> <span class="n">inc</span>
<span class="o">|</span> <span class="err">`</span><span class="o">--</span> <span class="n">tricks</span><span class="p">.</span><span class="n">rb</span>
<span class="err">`</span><span class="o">--</span> <span class="n">mylib</span><span class="p">.</span><span class="n">rb</span>
<span class="mi">2</span> <span class="n">directories</span><span class="p">,</span> <span class="mi">3</span> <span class="n">files</span>
</pre></div>
<p>如果我们把它提交(commit)到一个Git仓库中, 在Git中它们也许看起来就如下图: </p>
<p><img alt="示例" src="http://gitbook.liuhui998.com/assets/images/figure/objects-example.png" /></p>
<h5 id="_1">可以看到:<a class="headerlink" href="#_1" title="Permanent link">¶</a></h5>
<ul>
<li>每个目录都创建了 tree对象 (包括根目录), </li>
<li>每个文件都创建了一个对应的 blob对象 . </li>
<li>最后有一个 commit对象 来指向根tree对象(root of trees), </li>
<li>这样我们就可以追踪项目每一项提交内容.</li>
</ul>
<p><a href="http://gitbook.liuhui998.com/1_2.html">看到</a></p>
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<h4>Published</h4>
<time pubdate="pubdate" datetime="2015-03-29T00:00:00+08:00">Mar 29, 2015</time>
<h4>Category</h4>
<a class="category-link" href="/categories.html#It-ref">It</a>
<h4>Tags</h4>
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<li><a href="/tags.html#git-ref">git
<span>8</span>
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