You want to capture the catalog number, but instead you're matching the anchor text, and never even looking for what comes after it.

Try this.

/Catalog Number:\s+(\w+)/
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Update: (The first part of this node was posted from a smartphone, and pecking out markup and other symbols was unpleasant enough that I avoided my usual verbosity, which will now follow):

That anchors on "Catalog Number:" followed by any amount of whitespace, and then captures all contiguous "word" characters that follow, which would include alpha, numeric, and underscore. $1 would hold the catalog number in a successful match.

Anyone who mentioned you ought to parse HTML with a proper parsing module is correct though. Regexp solutions are fragile. It's strange that when we take our car to the mechanic we never say, "I want you to fix it using only a 12mm socket wrench." But people think nothing of coming for advice on parsing HTML, and in the same breath suggest that we ought to adapt our solutions to use only regular expressions, avoiding the vast array of other tools, many of which are more suitable for the task.

Don't use regexen to parse and extract from HTML. You'll almost certainly come a cropper.

Instead, use an appropriate HTML::(module). Search CPAN or ActiveState's PPM repository (depending on which Perl you're using) for the great range of modules ( for ex., CPAN://HTML::Extract] )which do the job.

And, please, wrap data (!!!) and code in <c>...</c> tags, as you're advised at the page where you enter your text.

I am new to parsing html pages using regular expressions. And I am wondering if some could point me into the right direction.

Yes. Don't.

As for trying to achieve your objective, I'd write:

print "Gotit! ($1)\n" if /Catalog Number: (PAL1001)/;
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I find it better and easier as far as the coding, to put the left hand side of the regex match into a list context and for example assign $catalog_num directly instead of fiddling with $1!

#!/usr/bin/perl -w
use strict;

my @lines = ( 'Catalog Number:  PAL1001',
              '  Catalog Number:PAL1001',
              'Catalog Number: Catalog Number:  PAL1001',
              'Catalog Number:  PAL1001Catalog Number:  PAL1001',
              'Cat Number:  PAL1001Catalog',
              'Catalog Number: 123PAL100');
              
foreach my $line (@lines)
{
   my ($catalog_num) = $line =~ /^\s*Catalog Number:\s*([A-Za-z]+\d+)/
+;
   
   if ($catalog_num)
   {
      print "$catalog_num\n"
   }
   else   
   {
      print "Bad Line!...$line\n";
   }
}

__END__

PAL1001
PAL1001
Bad Line!...Catalog Number: Catalog Number:  PAL1001
PAL1001
Bad Line!...Cat Number:  PAL1001Catalog
Bad Line!...Catalog Number: 123PAL100
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In the above, a valid catalog_num cannot be a numeric zero and so I can just test "if ($catalog_num)" instead of "if (defined $catalog_num)".