I have a repo which a submodule in it.
I can get the current hash of the submodule from the working directory easily:
cd submodule
git rev-list HEAD | head -n 1
However i am also interested in the hash at previous versions of the main repo. I can get it if i actually check out that version:
git checkout some_tag
cd submodule
git rev-list HEAD | head -n 1
However, i cannot use git checkout. Is there a way to obtain that hash without checking out the old tag?
Use git rev-parse
(which is also the correct tool for reading the value of HEAD
):
git rev-parse some_tag:submodule
This reads the gitlink entry from the tree object to which some_tag
can be resolved, using the supplied path. To see how it works, use:
tree=$(git rev-parse some_tag^{tree})
git ls-tree -r $tree
(the -r
option is only required if the submodule path is not at the top level of the repository). Note that the tree entry for the submodule is simply 160000 commit <hash> <path>
: this is how the superproject knows which commit hash ID to use in the submodule.
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