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+
+# 子模块
+
+开发个人网站的过程中需要用到主题仓库,所以会在一个仓库的里面嵌套另一个仓库,如果直接将子仓库加入版本管理,很多文件无法进行版本化,所以想到了子模块的操作
+
+## 创建子模块
+
+使用`git submodule`命令添加子模块
+
+    $ git submodule add git@github.com:zjZSTU/hexo-theme-next.git blogs/themes/next
+    Cloning into 'blogs/themes/next'...
+    remote: Enumerating objects: 1, done.
+    remote: Counting objects: 100% (1/1), done.
+    remote: Total 5402 (delta 0), reused 0 (delta 0), pack-reused 5401
+    Receiving objects: 100% (5402/5402), 5.29 MiB | 1.03 MiB/s, done.
+    Resolving deltas: 100% (3294/3294), done.
+    Checking connectivity... done.
+
+除了添加子仓库之外,还生成了一个配置文件`.gitmodules`
+
+    $ git status 
+    On branch dev
+    Your branch is ahead of 'origin/dev' by 1 commit.
+    (use "git push" to publish your local commits)
+    Changes to be committed:
+    (use "git reset HEAD <file>..." to unstage)
+
+        new file:   .gitmodules
+        new file:   blogs/themes/next
+
+`.gitmodules`里面保存了子模块的地址和远程仓库链接
+
+    $ cat .gitmodules 
+    [submodule "blogs/themes/next"]
+        path = blogs/themes/next
+        url = git@github.com:zjZSTU/hexo-theme-next.git
+
+## 管理子模块
+
+主仓库只能提示子模块中的文件修改,必须子模块自己进行添加和上传
+
+比如在`next`文件夹内新建文件`hellogit`
+
+    # 对于主模块而言
+    $ git status 
+    On branch dev
+    Your branch is up-to-date with 'origin/dev'.
+    Changes not staged for commit:
+        (use "git add <file>..." to update what will be committed)
+        (use "git checkout -- <file>..." to discard changes in working directory)
+        (commit or discard the untracked or modified content in submodules)
+
+	    modified:   next (untracked content)
+
+    no changes added to commit (use "git add" and/or "git commit -a")
+    # 对于子模块而言
+    $ git status 
+    HEAD detached at 0c5ed6f
+    Untracked files:
+        (use "git add <file>..." to include in what will be committed)
+
+	    hellogit
+
+    nothing added to commit but untracked files present (use "git add" to track)
+
+## 克隆子模块
+
+克隆主仓库后子模块的文件夹在但是没有文件,还需要进一步克隆子仓库
+
+    # 初始化本地配置文件
+    $ git submodule init
+    # 拉取远程仓库
+    $ git submodule update
+
+集成代码如下:
+
+    $ git submodule update --init --recursive
+
+## 更新子模块
+
+如果子模块有更新,可以进入子模块路径进行更新
+
+    $ git pull
+
+或者在主仓库更新所有子模块
+
+    $ git submodule foreach git pull 
+
+可能会遇到如下错误：
+
+```
+Entering 'blogs/themes/next'
+You are not currently on a branch.
+Please specify which branch you want to merge with.
+See git-pull(1) for details.
+    git pull <remote> <branch>
+Stopping at 'blogs/themes/next'; script returned non-zero status.
+The command "git submodule foreach git pull" failed and exited with 1 during .
+```
+
+需要指定哪个分支，要么修改更新语句如下：
+
+```
+$ git submodule foreach git pull origin master
+```
+
+要么设置远程关联分支
+
+```
+$ git branch --set-upstream-to=origin/remote_branch  your_branch
+# 或
+git branch --set-upstream your_branch origin/remote_branch
+```
+
+## 忽略子模块
+
+参考：[submodule.<name>.ignore ](https://git-scm.com/docs/gitmodules#Documentation/gitmodules.txt-submoduleltnamegtignore)
+
+当在子模块执行完成修改提交后，在主模块仍会显示子模块待提交
+
+```
+$ git status 
+On branch dev
+Your branch is up-to-date with 'origin/dev'.
+Changes not staged for commit:
+  (use "git add <file>..." to update what will be committed)
+  (use "git checkout -- <file>..." to discard changes in working directory)
+
+	modified:   blogs/themes/next (new commits)
+```
+
+需要修改`.gitmodule`的`ignore`属性，用于定义何种情况下使用`git status`或者`diff`命令会显示子模块的修改状况
+
+有`4`个可选的属性值
+
+1. `all`：子模块永远不会被认为是已修改的（但是当它处于暂存阶段时仍旧会在状态和提交命令的输出中）
+2. `dirty`：子模块工作树上的所有改变都会被忽略，只考虑子模块的`HEAD`与其在父项目中记录的状态之间的差异
+3. `untracked`：仅仅子模块未追踪的文件会被忽略。对于已追踪文件的提交差异和修改会显示
+4. `none`：默认选项。不会忽略所有对于子模块的修改，会显示所有的对于提交差异以及对于已追踪或未追踪的文件修改
+
+所以设置属性`ignore`为`all`就能忽略子模块变化
+
+```
+[submodule "blogs/themes/next"]
+	path = blogs/themes/next
+	url = https://github.com/zjZSTU/hexo-theme-next.git
+	ignore = all
+```
+
+## 相关阅读
+
+* [7.11 Git 工具 - 子模块](https://git-scm.com/book/zh/v2/Git-%E5%B7%A5%E5%85%B7-%E5%AD%90%E6%A8%A1%E5%9D%97)