nor do I know if my regular expression are correct

Would you like to find out? Here is how

use re 'debug';
$_ = q{<Hit_id>gnl|BL_ORD_ID|3665984</Hit_id>};
s/\>.\</\>REPLACE\</;
__END__
[download]

I don't think next is doing what I want

What is that (what do you want)? How did you learn about next?

See next, perlsyn, See "Loop control" section in Learn Perl in about 2 hours 30 minutes

See "Loop control" subsection in "Control Flow" section of Chapter 3 in the free book Modern Perl a loose description of how experienced and effective Perl 5 programmers work....You can learn this too.

So to learn about next you try like this

for my $ix (1..10){
    print "ix($ix)\n";
    if( $ix == 3 ){
        print "its threeee\n";
        next;
        print "PANCAKES\n";
    }
    print "its not threee\n";
}
__END__
[download]

After try the above two programs, what did you learn? What are you going to try next?