How can I get a git submodule's associated commit ID from a past commit in the parent clone?

user_143397 0
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Is there a way, short of actually checking out the parent commit, to determine a submodule's SHA-1 commit ID based on a commit ID in the parent clone? I know I can find the currently associated SHA-1 with git submodule.

Here's an example:

  • I have a clone with a single submodule foo that has changed several times in the last month.
  • I have a tag in the parent clone that is a few weeks old called released-1.2.3. I want to find out what the associated SHA-1 of foo was for this tagged commit.
  • I could simply check out released-1.2.3 and use git submodule to see, but I'm wondering if there's a way to do this without affecting the working tree, as I want to script it.

I want to do this because I want to construct a script to do a 'diff' on all changes within a submodule between two commits within the parent repository - i.e. "tell me what files changed within the submodule foo between these two commits in the parent."

diff git-submodules git
5 Answers

git ls-tree will do the job. But sometimes you should call it several times or use -r to show subentries recursively.

    ├─project
    │  └─submodules
    │      ├─submodule_a
    │      ├─submodule_b
    │      ├─...

For example, if you has such a project directory, and you want the commit id of submodule_a with an tag name in parent module.

git ls-tree v5.4.0

will give you the tree id of directory submodules, not commit id. It looks like as following.

040000 tree e542bc1b084a0394ff16452c27df6572366e0009    submodules

Just feed ls-tree with the tree id, and you will get the actual commit id of each submodule.

git ls-tree e542bc

You will get something like this.

160000 commit 0f253bf94e0345600cb7a234a24eeec8ee3533bd  submodule_a
160000 commit 0edcbaf94e034987cb4eeec8ee3533bd12349ade  submodule_b

Or just use 

git ls-tree v5.4.0 -r

to check all entries tree id or commit id.

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