在项目开发中，特别是web前端开发中，有非常多的开源第三方library，我们希望引用他们，同时也希望能够方便地保持这些第三方
开源repo的更新。另外一方面如果我们自己在开发一个网站的项目，这个项目一般分为前端和后端两个相对独立的子项目，特别是前端的repo可能在不同的项目*享，那么这时，你就可能希望将项目分开为前端和后端两个repo，如何管理这种情况呢？一个比较好的方案就是使用git的submodule功能。
假设我们的父repo在prepo目录，sumodule newtestrepo希望放在prepo/submods/newtestrepo这个目录,首先我们cd submods目录，
1. 在submods目录下执行：git submodule add https://github.com/cnweibo/newtestrepo.git 这个命令将在prepo目录下创建.gitmodules文件以及在prepo/submods/目录下创建newtestrepo目录用于保存newtestrepo内容。.gitmodules文件包含以下内容：
[submodule "submods/newtestrepo"]
path = submods/newtestrepo
url = https://github.com/cnweibo/newtestrepo.git
注意：在1.8版本git之前，上述命令必须在preop的root目录下执行！
2.执行git status，则发现有两个变更需要commit
(newcnweibo_branch)*$ git status
On branch newcnweibo_branch
Your branch is up-to-date with 'origin/newcnweibo_branch'. Changes to be committed:
(use "git reset HEAD <file>..." to unstage) new file: ../.gitmodules
new file: newtestrepo
3.执行git commit将增加submodule newtestrepo这个commit做一下提交
(newcnweibo_branch)*$ git commit -m "intro newtestrepo submodule"
[newcnweibo_branch 2bb87a3] intro newtestrepo submodule
files changed, insertions(+)
create mode .gitmodules
create mode submods/newtestrepo
4. git push 将上述修改放到preop的*库中去以便其他teammember使用
5. 如何在prepo这个项目中修改submodule呢？git checkout master 进入newtestrepo的master branch, 修改文件，commit，随后git push，注意这里的push是将submodule push到*库中。注意：submodule/newtestrepo目录下不再有.git目录，而只有一个.git文件，这一点很是奇妙！
在我们的submodule的目录中，你查看一下.git这个文件（不是文件夹哦！）的内容实际上指示列出来一个引用gitdir指向prepo的.git/modules/xxxdir/xxxrepo
(detached*)$ cat .git
gitdir: ../../.git/modules/submods/newtestrepo
6. 注意，这时如果我们到prepo的目录中，git status发现我们又有了两个没有commit的commit。
随后我们需要将prepo也做push以便将上述两个commits递交.
之所以在submodule中修改并且push后还要在prepo中push是因为我们的父repo其实是引用了子module的一个snapshot，子module修改后，父repo并没有修改对版本的引用，因此需要commit来反映这个变化。
7.当我们另外一个teammember clone这个prepo时，注意，prepo里面所包含的submodule本身目录都为空！
*$ pwd
/home/cabox/workspace/testgit
*$ git clone https://github.com/cnweibo/githubtest.git
Cloning into 'githubtest'...
remote: Counting objects: , done.
remote: Total (delta ), reused (delta ), pack-reused
Unpacking objects: % (/), done.
Checking connectivity... done.
*$ ls
githubtest
*$ cd githubtest/
(newcnweibo_branch)$ ls
localconfig newweibobranchfile readmegithub submods
(newcnweibo_branch)$ git status
On branch newcnweibo_branch
Your branch is up-to-date with 'origin/newcnweibo_branch'. nothing to commit, working directory clean
(newcnweibo_branch)$ cd submods/
(newcnweibo_branch)$ ls
newtestrepo
(newcnweibo_branch)$ cd newtestrepo/
(newcnweibo_branch)$ ls
(newcnweibo_branch)$ ls -la
total
drwxrwxr-x cabox cabox May : .
drwxrwxr-x cabox cabox May : ..
(newcnweibo_branch)$
但是我们的prepo: githubtest本身却有一个文件.gitmodules,它列出了在prepo中是如何引用sub module的
(newcnweibo_branch)$ pwd
/home/cabox/workspace/testgit/githubtest
(newcnweibo_branch)$ ls -la
total
drwxrwxr-x cabox cabox May : .
drwxrwxr-x cabox cabox May : ..
drwxrwxr-x cabox cabox May : .git
-rw-rw-r-- cabox cabox May : .gitmodules
-rw-rw-r-- cabox cabox May : localconfig
-rw-rw-r-- cabox cabox May : newweibobranchfile
-rw-rw-r-- cabox cabox May : readmegithub
drwxrwxr-x cabox cabox May : submods
(newcnweibo_branch)$ cat .gitmodules
[submodule "submods/newtestrepo"]
path = submods/newtestrepo
url = git@github.com:cnweibo/newtestrepo.git
8.为了能够正常使用submodule,我们必须在新clone的prepo中执行 git submodule init命令，执行该命令时：git将通过检查.gitmodules文件中的
[submodule "submods/newtestrepo"] 这个section，为每一个submodule都正在prepo的.git/config文件中增加一条
[submodule "submods/newtestrepo"]
url = git@github.com:cnweibo/newtestrepo.git 信息！
(newcnweibo_branch)$ pwd
/home/cabox/workspace/testgit/githubtest
(newcnweibo_branch)$ git submodule init
Submodule 'submods/newtestrepo' (git@github.com:cnweibo/newtestrepo.git) registered for path 'su
bmods/newtestrepo'
(newcnweibo_branch)$ ls -la
total
drwxrwxr-x cabox cabox May : .
drwxrwxr-x cabox cabox May : ..
drwxrwxr-x cabox cabox May : .git
-rw-rw-r-- cabox cabox May : .gitmodules
-rw-rw-r-- cabox cabox May : localconfig
-rw-rw-r-- cabox cabox May : newweibobranchfile
-rw-rw-r-- cabox cabox May : readmegithub
drwxrwxr-x cabox cabox May : submods
(newcnweibo_branch)$ cat .git/
HEAD config hooks/ info/ objects/ refs/
branches/ description index logs/ packed-refs
(newcnweibo_branch)$ cat .git/config
[core]
repositoryformatversion =
filemode = true
bare = false
logallrefupdates = true
[remote "origin"]
url = https://github.com/cnweibo/githubtest.git
fetch = +refs/heads/*:refs/remotes/origin/*
[branch "newcnweibo_branch"]
remote = origin
merge = refs/heads/newcnweibo_branch
[submodule "submods/newtestrepo"]
url = git@github.com:cnweibo/newtestrepo.git
(newcnweibo_branch)$
9.随后我们在prepo再执行git submodule update，这时git将通过Internet把所有的submodule clone进入我们的子目录中（由.gitmodules文件来决定放到哪个子目录中）
(newcnweibo_branch)$ pwd
/home/cabox/workspace/testgit/githubtest
(newcnweibo_branch)$ ls -la submods/newtestrepo/
total
drwxrwxr-x cabox cabox May : .
drwxrwxr-x cabox cabox May : ..
(newcnweibo_branch)$ git submodule update
Cloning into 'submods/newtestrepo'...
Warning: Permanently added 'github.com,192.30.252.129' (RSA) to the list of known hosts.
Permission denied (publickey).
fatal: Could not read from remote repository. Please make sure you have the correct access rights
and the repository exists.
Clone of 'git@github.com:cnweibo/newtestrepo.git' into submodule path 'submods/newtestrepo' failed
$ ssh -T git@github.com
Hi kidsit! You've successfully authenticated, but GitHub does not provide shell access.
$ exit
exit
(newcnweibo_branch)*$ pwd
/home/cabox/workspace/testgit/githubtest
(newcnweibo_branch)*$ git submodule update
Cloning into 'submods/newtestrepo'...
Warning: Permanently added the RSA host key for IP address '192.30.252.130' to the list of known hosts.
remote: Counting objects: , done.
remote: Compressing objects: % (/), done.
remote: Total (delta ), reused (delta ), pack-reused
Receiving objects: % (/), done.
Checking connectivity... done.
Submodule path 'submods/newtestrepo': checked out '6c495d0229fcd15fd7e0bb3cded878d0692988a5'
(newcnweibo_branch)$ git submodule update^C
(newcnweibo_branch)$ ls -la submods/newtestrepo/
.git README.md changefromprepo
(newcnweibo_branch)$ ls -la submods/newtestrepo/
.git README.md changefromprepo
(newcnweibo_branch)$ ls -la submods/newtestrepo/
total
drwxrwxr-x cabox cabox May : .
drwxrwxr-x cabox cabox May : ..
-rw-rw-r-- cabox cabox May : .git
-rw-rw-r-- cabox cabox May : README.md
-rw-rw-r-- cabox cabox May : changefromprepo
(newcnweibo_branch)$ cat submods/newtestrepo/.git
gitdir: ../../.git/modules/submods/newtestrepo