我想在这里补充一个答案，它实际上只是其他答案的综合，但我认为它可能更完整。

有了这两个东西，就有了Git子模块。

Your .gitmodules has an entry like so: [submodule "SubmoduleTestRepo"] path = SubmoduleTestRepo url = https://github.com/jzaccone/SubmoduleTestRepo.git You have a submodule object (named SubmoduleTestRepo in this example) in your Git repository. GitHub shows these as "submodule" objects. Or do git submodule status from a command line. Git submodule objects are special kinds of Git objects, and they hold the SHA information for a specific commit. Whenever you do a git submodule update, it will populate your submodule with content from the commit. It knows where to find the commit because of the information in the .gitmodules. Now, all the -b does is add one line in your .gitmodules file. So following the same example, it would look like this: [submodule "SubmoduleTestRepo"] path = SubmoduleTestRepo url = https://github.com/jzaccone/SubmoduleTestRepo.git branch = master Note: only branch name is supported in a .gitmodules file, but SHA and TAG are not supported! (instead of that, the branch's commit of each module can be tracked and updated using "git add .", for example like git add ./SubmoduleTestRepo, and you do not need to change the .gitmodules file each time) The submodule object is still pointing at a specific commit. The only thing that the -b option buys you is the ability to add a --remote flag to your update as per Vogella's answer: git submodule update --remote Instead of populating the content of the submodule to the commit pointed to by the submodule, it replaces that commit with the latest commit on the master branch, THEN it populates the submodule with that commit. This can be done in two steps by djacobs7 answer. Since you have now updated the commit the submodule object is pointing to, you have to commit the changed submodule object into your Git repository. git submodule add -b is not some magically way to keep everything up to date with a branch. It is simply adds information about a branch in the .gitmodules file and gives you the option to update the submodule object to the latest commit of a specified branch before populating it.

我的.gitconfig文件中有这个。它仍然是一份草案，但目前证明是有用的。它帮助我总是将子模块重新连接到它们的分支。

[alias]

######################
#
# Submodules aliases
#
######################

# git sm-trackbranch: places all submodules on their respective branch specified in .gitmodules
# This works if submodules are configured to track a branch, i.e if .gitmodules looks like:
# [submodule "my-submodule"]
#   path = my-submodule
#   url = git@wherever.you.like/my-submodule.git
#   branch = my-branch
sm-trackbranch = "! git submodule foreach -q --recursive 'branch=\"$(git config -f $toplevel/.gitmodules submodule.$name.branch)\"; git checkout $branch'"

# sm-pullrebase:
# - pull --rebase on the master repo
# - sm-trackbranch on every submodule
# - pull --rebase on each submodule
#
# Important note:
# - have a clean master repo and subrepos before doing this!
# - this is *not* equivalent to getting the last committed
#   master repo + its submodules: if some submodules are tracking branches
#   that have evolved since the last commit in the master repo,
#   they will be using those more recent commits!
#
#   (Note: On the contrary, git submodule update will stick
#   to the last committed SHA1 in the master repo)
sm-pullrebase = "! git pull --rebase; git submodule update; git sm-trackbranch ; git submodule foreach 'git pull --rebase' "

# git sm-diff will diff the master repo *and* its submodules
sm-diff = "! git diff && git submodule foreach 'git diff' "

# git sm-push will ask to push also submodules
sm-push = push --recurse-submodules=on-demand

# git alias: list all aliases
# useful in order to learn git syntax
alias = "!git config -l | grep alias | cut -c 7-"

Git子模块有点奇怪——它们总是处于“分离头”模式——它们不会像你期望的那样更新到分支上的最新提交。

不过，当你仔细思考时，这确实是有道理的。假设我用子模块bar创建了存储库foo。我推送我的更改并告诉您从存储库foo中提交a7402be。

然后想象一下，在您可以克隆之前，有人将更改提交到存储库栏。

当您从存储库foo签出commit a7402be时，您希望得到与我推送的相同的代码。这就是为什么子模块不会更新，直到你显式地告诉它们，然后进行新的提交。

我个人认为子模块是Git中最令人困惑的部分。有很多地方可以比我更好地解释子模块。我推荐Scott Chacon的Pro Git。

注意:Git 1.8.2增加了跟踪分支的可能性。下面是一些答案。

习惯这一点有点令人困惑，但子模块并不在分支上。正如您所说，它们只是指向子模块存储库的特定提交的指针。

这意味着，当其他人签出你的存储库，或提取你的代码，并进行git子模块更新时，子模块将被签出到特定的提交。

这对于不经常更改的子模块非常有用，因为这样项目中的每个人都可以在同一次提交时拥有子模块。

如果你想移动子模块到一个特定的标签:

cd submodule_directory
git checkout v1.0
cd ..
git add submodule_directory
git commit -m "moved submodule to v1.0"
git push

然后，另一个希望将submodule_directory更改为该标记的开发人员执行此操作

git pull
git submodule update --init

Git拉修改提交他们的子模块目录指向。Git子模块update实际上合并到新代码中。

为了切换子模块的分支(假设你已经将子模块作为存储库的一部分):

CD到包含子模块的存储库的根目录 打开.gitmodules进行编辑 在path =…url =…对于每个子模块，它说branch = your-branch;保存文件。gitmodules。 然后在不改变目录的情况下执行$ git子模块update——remote

.．.对于这样修改的每个子模块，这应该拉入指定分支上的最新提交。

一个我如何使用Git子模块的例子。

创建一个新的存储库 然后将另一个存储库克隆为子模块 然后让该子模块使用一个名为V3.1.2的标记 然后我们承诺。

它看起来有点像这样:

git init 
vi README
git add README
git commit 
git submodule add git://github.com/XXXXX/xxx.yyyy.git stm32_std_lib
git status

git submodule init
git submodule update

cd stm32_std_lib/
git reset --hard V3.1.2 
cd ..
git commit -a

git submodule status 

也许它有帮助(即使我使用标记而不是分支)?