"Don't use [] around ranges in tr, it replaces literal square brackets."
this introduces another warning:
"Use '[:lower:]' to support accents and foreign alphabets."
This is more a style thingy because we really want to only catch A-Z.
work around this by using a shellcheck-directive and a comment
that the [:lower:] will not work with e.g. busybox-ash.
if we later really want to use [:lower:], we should use 'sed' for that.
Bastian Bittorf