my $string = q{"string (12" or 1 foot or 1') into 6" MySQL varchar"};

benchmark(
        shift,
        q{"string (12"" or 1 foot or 1') into 6"" MySQL varchar"},

        'substr' => sub {
                my $t = $string;
                substr($t, 1, -1) =~ s/"/""/g;
                $t
        },

        's///' => sub {
                my $t = $string;
                $t =~ s/(?<=.)"(?=.)/""/g;
                $t
        },

        'index' => sub {
                my $t = $string;
                local $_ = 1;
                while( ($_ = index($t,'"',$_)) !=-1
                               and ++$_ < length($t)
                                      ){
                              substr($t,$_++,0,'"');
                }
                $t
        },
);