Typically you would first remove all tracked files from the working
tree using this command:
+Submodules
+~~~~~~~~~~
+Only submodules using a gitfile (which means they were cloned
+with a git version 1.7.8 or newer) will be removed from the work
+tree, as their repository lives inside the .git directory of the
+superproject. If a submodule (or one of those nested inside it)
+still uses a .git directory, `git rm` will fail - no matter if forced
+or not - to protect the submodule's history.
+
+A submodule is considered up-to-date when the HEAD is the same as
+recorded in the index, no tracked files are modified and no untracked
+files that aren't ignored are present in the submodules work tree.
+Ignored files are deemed expendable and won't stop a submodule's work
+tree from being removed.
+
----------------
git ls-files -z | xargs -0 rm -f
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