Checks if a given refname is acceptable, and exits with a non-zero status if it is not.

# To check the format of the specified refname:
git check-ref-format <refs/head/refname>

# To print the name of the last branch checked out:
git check-ref-format --branch @{-1}

# To normalize a refname:
git check-ref-format --normalize <refs/head/refname>