If you get a warning that you don't understand it's always worth adding "use diagnostics" to your program to get a more details error. You'll see something like this:

False [] range "%s" in regex; marked by <-- HERE in m/%s/
(W regexp) A character class range must start and end at a literal character, not another character class like \d or :alpha:. The "-" in your false range is interpreted as a literal "-". Consider quoting the "-", "\-". The <-- HERE shows in the regular expression about where the problem was discovered. See perlre.

--
<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg