tr -[cC]s '[:upper:]' '[:lower:]' case (or vice versa): chars taken from s2 can be different this time due to lack of complex upper/lower processing, so fill string2 again to not miss some.
tr -[cC]s '[:upper:]' '[:lower:]' case (or vice versa): chars taken from s2 can be different this time due to lack of complex upper/lower processing, so fill string2 again to not miss some.