use strict;
use warnings;

my $string = <<'EOT';
start
start
start
go
one
end
start
start
start
go
two
end
EOT

my $rxGroup = qr
   {(?isx)
       (
           start
           (?!\nstart)
           .+?
           end
       )
   };

print qq{$1\n\n} while $string =~ m{$rxGroup}g;

##</code><code>##

start
go
one
end

start
go
two
end