use YAPE::Regex::Explain; print YAPE::Regex::Explain->new( '\.([^.]+)$' )->explain; __END__ The regular expression: (?-imsx:\.([^.]+)$) 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): ---------------------------------------------------------------------- \. '.' ---------------------------------------------------------------------- ( group and capture to \1: ---------------------------------------------------------------------- [^.]+ any character except: '.' (1 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of \1 ---------------------------------------------------------------------- $ before an optional \n, and the end of the string ---------------------------------------------------------------------- ) end of grouping ----------------------------------------------------------------------