local $/ = "\nend\n";
while ( my $data = <DATA> ) {
    $data =~ s/^.*start/start/is;
    print $data;
    print '=' x 10, "\n";
}

__DATA__
start
start
start
go
one
end
start
start
start
go
two
end

##</code><code>##

start
go
one
end
==========
start
go
two
end
==========

##</code><code>##

my $data = '';
while ( my $line = <DATA> ) {
    $data .= $line;
    if ( $line =~ /^end$/i ) {
        $data =~ s/^.*start/start/is;
        print $data;
        print '=' x 10, "\n";
        $data = '';
    }
}