my $string = qw!"This is \"data\""!;

##</code><code>##

$string =~ /"((?:\\"|[^"])*)"/;

##</code><code>##

$string =~ /"           # first quote
             (          # capture to $1
               (?:      #   non-capturing parens
                  \\"   #   an escaped quote
                  |     #   or
                  [^"]  #   a non-quote
               )*       #   end grouping (zero or more of above)
             )          # end capture
            "/x;        # last quote

##</code><code>##

$string =~ /"((?:\\["\\]|[^"])*)"/;