C:\>perl -MYAPE::Regex::Explain -le"print YAPE::Regex::Explain->new(qr/[^[:print:]]/)->explain" The regular expression: (?-imsx:[^[:print:]]) 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): ---------------------------------------------------------------------- [^[:print:]] any character except: alphanumeric, punctuation, and whitespace characters ---------------------------------------------------------------------- ) end of grouping ----------------------------------------------------------------------