When you call $cgi->Vars, you don't get a normal hashref.

You mean array context list context, but yes, that does give you a list that you can make into your own normal hash. Here's the sub definition:

sub Vars {
    my $q = shift;
    my %in;
    tie(%in,CGI,$q);
    return %in if wantarray;
    return \%in;
}
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Maybe I've mis-understood you -- I made the code less fancy and used a hash instead of a hashref, as shown below, and got the sme result.

    for ( 1..9 ) {
    
      my $last = "last_name$_";
      my $first = "first_name$_";
      my %h;
      
      if ( length($vars->{$last}) && length($vars->{$last}) ) {
      
        $h{'last_name'} = $vars->{$last};
        $h{'First_name'} = $vars->{$first};
      
      } else {
      
        #  Leave a blank one at the end.
        
        $h{'last_name'} = '';
        $h{'First_name'} = '';
        
        last;
      }
      push ( @reg_array, \%h );
    }
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I guess I don't understand your answer.

I'm able to get the information from $vars just fine, but it seems putting it back onto the form is a problem.

In your original code, you get a hashref back from $cgi->Vars, and then you try to put @reg_array into it as if it were a normal hashref. That would work, except that $vars that comes back from $cgi->Vars is not a hashref, but rather a tied variable that CGI generated.

I can't tell if the code you show here still has that problem because you didn't show that part. If it does, a quick fix would be to change that line where you call $cgi->Vars to this:

my %vars = $cgi->Vars;
my $vars = \%vars;
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