1.Using another project while maintaining independent history. Submodules allow you to contain the working tree of another project within your own working tree while keeping the history of both projects separate. Also, since submodules are fixed to an arbitrary version, the other project can be independently developed without affecting the superproject, allowing the superproject project to fix itself to new versions only when desired.

2.Splitting a (logically single) project into multiple repositories and tying them back together. This can be used to overcome current limitations of Git’s implementation to have finer grained access:

•The command line for those commands that support taking submodules as part of their pathspecs. Most commands have a boolean flag --recurse-submodules which specify whether to recurse into submodules. Examples are grep and checkout. Some commands take enums, such as fetch and push, where you can specify how submodules are affected.

•The configuration inside the submodule. This includes $GIT_DIR/config in the submodule, but also settings in the tree such as a .gitattributes or .gitignore files that specify behavior of commands inside the submodule.

For example an effect from the submodule’s .gitignore file would be observed when you run git status --ignore-submodules=none in the superproject. This collects information from the submodule’s working directory by running status in the submodule while paying attention to the .gitignore file of the submodule.

The submodule’s $GIT_DIR/config file would come into play when running git push --recurse-submodules=check in the superproject, as this would check if the submodule has any changes not published to any remote. The remotes are configured in the submodule as usual in the $GIT_DIR/config file.

•The configuration file $GIT_DIR/config in the superproject. Git only recurses into active submodules (see "ACTIVE SUBMODULES" section below).

If the submodule is not yet initialized, then the configuration inside the submodule does not exist yet, so where to obtain the submodule from is configured here for example.

•The .gitmodules file inside the superproject. A project usually uses this file to suggest defaults for the upstream collection of repositories for the mapping that is required between a submodule’s name and its path.

This file mainly serves as the mapping between the name and path of submodules in the superproject, such that the submodule’s Git directory can be located.

If the submodule has never been initialized, this is the only place where submodule configuration is found. It serves as the last fallback to specify where to obtain the submodule from.

•The basic form described in DESCRIPTION with a Git directory, a working directory, a gitlink, and a .gitmodules entry.

•"Old-form" submodule: A working directory with an embedded .git directory, and the tracking gitlink and .gitmodules entry in the superproject. This is typically found in repositories generated using older versions of Git.

It is possible to construct these old form repositories manually.

When deinitialized or deleted (see below), the submodule’s Git directory is automatically moved to $GIT_DIR/modules/<name>/ of the superproject.

•Deinitialized submodule: A gitlink, and a .gitmodules entry, but no submodule working directory. The submodule’s Git directory may be there as after deinitializing the Git directory is kept around. The directory which is supposed to be the working directory is empty instead.

A submodule can be deinitialized by running git submodule deinit. Besides emptying the working directory, this command only modifies the superproject’s $GIT_DIR/config file, so the superproject’s history is not affected. This can be undone using git submodule init.

•Deleted submodule: A submodule can be deleted by running git rm <submodule path> && git commit. This can be undone using git revert.

The deletion removes the superproject’s tracking data, which are both the gitlink entry and the section in the .gitmodules file. The submodule’s working directory is removed from the file system, but the Git directory is kept around as it to make it possible to checkout past commits without requiring fetching from another repository.

To completely remove a submodule, manually delete $GIT_DIR/modules/<name>/.

1.if submodule.<name>.active is set to true

or

2.if the submodule’s path matches the pathspec in submodule.active

or

3.if submodule.<name>.url is set.

[submodule "foo"]
  active = false
  url = https://example.org/foo
[submodule "bar"]
  active = true
  url = https://example.org/bar
[submodule "baz"]
  url = https://example.org/baz

[submodule "foo"]
  active = true
  url = https://example.org/foo
[submodule "bar"]
  url = https://example.org/bar
[submodule "baz"]
  url = https://example.org/baz
[submodule "bob"]
  ignore = true
[submodule]
  active = b*
  active = :(exclude) baz

# Add a submodule
git submodule add <URL> <path>

# Occasionally update the submodule to a new version:
git -C <path> checkout <new version>
git add <path>
git commit -m "update submodule to new version"

# See the list of submodules in a superproject
git submodule status

# See FORMS on removing submodules

# Enable recursion for relevant commands, such that
# regular commands recurse into submodules by default
git config --global submodule.recurse true

# Unlike most other commands below, clone still needs
# its own recurse flag:
git clone --recurse <URL> <directory>
cd <directory>

# Get to know the code:
git grep foo
git ls-files --recurse-submodules

Note

git ls-files also requires its own --recurse-submodules flag.

# Get new code
git fetch
git pull --rebase

# Change worktree
git checkout
git reset