I'm not sure what you are trying to accomplish. The natural thing to think about with x=123 y=456 type pairs is a hash. Below I show how to generate that hash with match global. You could check if the "lo" key is defined or not.

Stay away from this $& stuff as that will slow all regexes down. And its very seldom needed. If you just need to check if: lo="XYZZY" is on the line, the regex is easier than below. But this a general name="value" solution.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

while (<DATA>)
{
   next unless (/^<dsk1/);
   my %hash = m/(\w+)\s*=\s*"(.*?)"/g;
   
   next unless keys %hash;   #skip blank hashes (no pairs)
   print "name=value pairs:\n";
   foreach my $name (sort keys %hash)
   {
       print "   $name=>$hash{$name}\n";
   }
   print "\n";
}

=prints:
name=value pairs:
   id=>123
   lo=>1
   rb=>This is a long rb.
   to=>abc

name=value pairs:
   id=>456
   lo=>2
   rb=>Short rb
   to=>def

name=value pairs:
   id=>789
   lo=>3
   rb=>Medium long rb
   to=>ghi

name=value pairs:
   id=>987
   lo=>6
   rb=>This should be a match
   to=>mno

name=value pairs:
   id=>FFF
   lo=>7
   rb=>This is a very, very, very long are-bee.
   to=>pqr
=cut

__DATA__
<dsk1 line1 id="123" lo="1" to="abc" rb="This is a long rb."
<dsk1 line2 id="456" lo="2" to="def" rb="Short rb"
<dsk1 line3 id="789" lo="3" to="ghi" rb="Medium long rb"
<dsk2 line4 
<dsk2 line5 id="555" lo="5" to="jkl" rb="should not match"
<dsk1 Line6 id="987" lo="6" to="mno" rb="This should be a match"
<dsk1 line7 id="FFF" lo="7" to="pqr" rb="This is a very, very, very lo
+ng are-bee."
[download]

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