perlop.txt

    The following escape sequences are available in constructs that
    interpolate, but not in transliterations.

        \l          lowercase next character only
        \u          titlecase (not uppercase!) next character only
        \L          lowercase all characters till \E or end of string
        \U          uppercase all characters till \E or end of string
        \F          foldcase all characters till \E or end of string
        \Q          quote (disable) pattern metacharacters till \E or
                    end of string
        \E          end either case modification or quoted section
                    (whichever was last seen)