在專案開發中，特別是web前端開發中，有非常多的開源第三方library，我們希望引用他們，同時也希望能夠方便地保持這些第三方
開源repo的更新。另外一方面如果我們自己在開發一個網站的專案，這個專案一般分為前端和後端兩個相對獨立的子專案，特別是前端的repo可能在不同的專案中共享，那麼這時，你就可能希望將專案分開為前端和後端兩個repo，如何管理這種情況呢？一個比較好的方案就是使用git的submodule功能。
假設我們的父repo在prepo目錄，sumodule newtestrepo希望放在prepo/submods/newtestrepo這個目錄,首先我們cd submods目錄，
1. 在submods目錄下執行：git submodule add https://github.com/cnweibo/newtestrepo.git 這個命令將在prepo目錄下建立.gitmodules檔案以及在prepo/submods/目錄下建立newtestrepo目錄用於儲存newtestrepo內容。.gitmodules檔案包含以下內容：
[submodule "submods/newtestrepo"] path = submods/newtestrepo url = https://github.com/cnweibo/newtestrepo.git
注意：在1.8版本git之前，上述命令必須在preop的root目錄下執行！
2.執行git status，則發現有兩個變更需要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.執行git commit將增加submodule newtestrepo這個commit做一下提交
(newcnweibo_branch)*$ git commit -m "intro newtestrepo submodule" [newcnweibo_branch 2bb87a3] intro newtestrepo submodule 2 files changed, 4 insertions(+) create mode 100644 .gitmodules create mode 160000 submods/newtestrepo
4. git push 將上述修改放到preop的中央庫中去以便其他teammember使用
5. 如何在prepo這個專案中修改submodule呢？git checkout master 進入newtestrepo的master branch, 修改檔案，commit，隨後git push，注意這裡的push是將submodule push到中央庫中。注意：submodule/newtestrepo目錄下不再有.git目錄，而只有一個.git檔案，這一點很是奇妙！
在我們的submodule的目錄中，你檢視一下.git這個檔案（不是資料夾哦！）的內容實際上指示列出來一個引用gitdir指向prepo的.git/modules/xxxdir/xxxrepo
(detached*)$ cat .git gitdir: ../../.git/modules/submods/newtestrepo
6. 注意，這時如果我們到prepo的目錄中，git status發現我們又有了兩個沒有commit的commit。
隨後我們需要將prepo也做push以便將上述兩個commits遞交.
之所以在submodule中修改並且push後還要在prepo中push是因為我們的父repo其實是引用了子module的一個snapshot，子module修改後，父repo並沒有修改對版本的引用，因此需要commit來反映這個變化。
7.當我們另外一個teammember clone這個prepo時，注意，prepo裡面所包含的submodule本身目錄都為空！
*$ pwd /home/cabox/workspace/testgit *$ git clone https://github.com/cnweibo/githubtest.git Cloning into 'githubtest'... remote: Counting objects: 53, done. remote: Total 53 (delta 0), reused 0 (delta 0), pack-reused 53 Unpacking objects: 100% (53/53), 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 8 drwxrwxr-x 2 cabox cabox 4096 May 30 01:08 . drwxrwxr-x 3 cabox cabox 4096 May 30 01:08 .. (newcnweibo_branch)$
但是我們的prepo: githubtest本身卻有一個檔案.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 32 drwxrwxr-x 4 cabox cabox 4096 May 30 01:08 . drwxrwxr-x 3 cabox cabox 4096 May 30 01:08 .. drwxrwxr-x 8 cabox cabox 4096 May 30 01:11 .git -rw-rw-r-- 1 cabox cabox 108 May 30 01:08 .gitmodules -rw-rw-r-- 1 cabox cabox 1747 May 30 01:08 localconfig -rw-rw-r-- 1 cabox cabox 66 May 30 01:08 newweibobranchfile -rw-rw-r-- 1 cabox cabox 185 May 30 01:08 readmegithub drwxrwxr-x 3 cabox cabox 4096 May 30 01:08 submods (newcnweibo_branch)$ cat .gitmodules [submodule "submods/newtestrepo"] path = submods/newtestrepo url = git@github.com:cnweibo/newtestrepo.git
8.為了能夠正常使用submodule,我們必須在新clone的prepo中執行 git submodule init命令，執行該命令時：git將通過檢查.gitmodules檔案中的
[submodule "submods/newtestrepo"] 這個section，為每一個submodule都正在prepo的.git/config檔案中增加一條
[submodule "submods/newtestrepo"]
url = git@github.com:cnweibo/newtestrepo.git 資訊！
(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 32 drwxrwxr-x 4 cabox cabox 4096 May 30 01:08 . drwxrwxr-x 3 cabox cabox 4096 May 30 01:08 .. drwxrwxr-x 8 cabox cabox 4096 May 30 01:17 .git -rw-rw-r-- 1 cabox cabox 108 May 30 01:08 .gitmodules -rw-rw-r-- 1 cabox cabox 1747 May 30 01:08 localconfig -rw-rw-r-- 1 cabox cabox 66 May 30 01:08 newweibobranchfile -rw-rw-r-- 1 cabox cabox 185 May 30 01:08 readmegithub drwxrwxr-x 3 cabox cabox 4096 May 30 01:08 submods (newcnweibo_branch)$ cat .git/ HEAD config hooks/ info/ objects/ refs/ branches/ description index logs/ packed-refs (newcnweibo_branch)$ cat .git/config [core] repositoryformatversion = 0 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.隨後我們在prepo再執行git submodule update，這時git將通過Internet把所有的submodule clone進入我們的子目錄中（由.gitmodules檔案來決定放到哪個子目錄中）
(newcnweibo_branch)$ pwd /home/cabox/workspace/testgit/githubtest (newcnweibo_branch)$ ls -la submods/newtestrepo/ total 8 drwxrwxr-x 2 cabox cabox 4096 May 30 01:08 . drwxrwxr-x 3 cabox cabox 4096 May 30 01:08 .. (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: 6, done. remote: Compressing objects: 100% (3/3), done. remote: Total 6 (delta 0), reused 3 (delta 0), pack-reused 0 Receiving objects: 100% (6/6), 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 20 drwxrwxr-x 2 cabox cabox 4096 May 30 01:32 . drwxrwxr-x 3 cabox cabox 4096 May 30 01:32 .. -rw-rw-r-- 1 cabox cabox 47 May 30 01:32 .git -rw-rw-r-- 1 cabox cabox 14 May 30 01:32 README.md -rw-rw-r-- 1 cabox cabox 29 May 30 01:32 changefromprepo (newcnweibo_branch)$ cat submods/newtestrepo/.git gitdir: ../../.git/modules/submods/newtestrepo