Include submodules as well in git checkout-index

Question

Is there a way to copy files from the submodules as well when doing git checkout-index?

I already checked the documentation of git checkout-index but it makes no mention of submodules

Answer 1

Neither checkout-index.c, t/t2006-checkout-index-basic.sh nor Documentation/git-checkout-index.txt mention submodules.
That was confirmed/discussed in this issue (2010) or this one (2015-2016).

So (as commented) git submodule foreach remains the best option:

 git submodule foreach --recursive 'git checkout-index'