use YAPE::Regex::Explain; print YAPE::Regex::Explain->new(qr/999[89]\$/)->explain(); __END__ The regular expression: (?-imsx:999[89]\$) matches as follows: NODE EXPLANATION ---------------------------------------------------------------------- (?-imsx: group, but do not capture (case-sensitive) (with ^ and $ matching normally) (with . not matching \n) (matching whitespace and # normally): ---------------------------------------------------------------------- 999 '999' ---------------------------------------------------------------------- [89] any character of: '8', '9' ---------------------------------------------------------------------- \$ '$' ---------------------------------------------------------------------- ) end of grouping ----------------------------------------------------------------------