use strict;
use warnings;

my $s = '"toto"';
if ($s =~ 
    m[^
        (?<!\\)"
        (
            (
                (?<=\\)"|[^"]
            )+                         # $2
        )                              # $1
        (?<!\\)"
    $]x
) {
  print "It matches!\n";
  print $1 . "\n";
  print $2 . "\n";
}