uc EXPR
    uc      Returns an uppercased version of EXPR. This is the internal
            function implementing the "\U" escape in double-quoted strings.
            It does not attempt to do titlecase mapping on initial letters.
            See "ucfirst" for that.

            If EXPR is omitted, uses $_.

            This function behaves the same way under various pragma, such as
            in a locale, as "lc" does.