As nearly everyone has pointed out you almost certainly want to this with a module such as HTML::Parser, the following is an example of how you would achieve this for your snippet of HTML:

#!/usr/bin/perl
 
use strict;
use warnings;
 
my $text= "<td class=sp></td><td>Hello</td><td class=sp></td><td>Bye</
+td><td class=sp>";
 
 
use HTML::Parser;
my $parser = HTML::Parser->new( start_h => [ \&start,"self,tag,attr" ]
+,
                                start_document_h => [ \&init,"self"]);
 
                                                                      
+          
$parser->parse($text);
 
foreach my $item ( @{$parser->{_items}} )
{
   print $item,"\n";
}
 
sub init
{
   my ( $self ) = @_;
   $self->{_items} = [];
}
 
sub start
{
    my ( $self, $tag, $attribs) = @_;
 
    if ( $tag eq 'td' && !exists $attribs->{class} )
    {
       $self->handler(text => \&get_text,"self,dtext" );
       $self->handler(end  => \&end,"self,tag");
    }
}
 
sub get_text
{
    my ( $self, $text) = @_;
 
    $self->{_text} .= $text;
}
 
sub end
{
   my ( $self, $tag ) = @_;
   if ( $tag eq '/td' )
   {
      $self->handler(text => '' );
      $self->handler(end => '');
      push @{$self->{_items}}, $self->{_text};
      $self->{_text} = '';
   }
}
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/J\