Are you sure you want to use a regex to do this? I think it's much more natural to use unpack (or even split, possibly) to do what you're trying to do.

Update: I suppose I should mention that the *reason* it would be more natural to use unpack is because your columns are fixed-width columns. Unpack is great for extracting columnar data formatted in this way...

Try this to see if it works for you:

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my %hash = ( 'CA12DE' => 1 );

my  $line = 'Box of Joe     CA12DE    12345';
my @data = unpack 'A15A10A9', $line;
print Dumper(\@data);

my $searchkey = $data[1];
if (exists($hash{$searchkey})) {
  print qq(searchkey "$searchkey" exists in the hash...\n);
}
[download]

__OUTPUT__
$VAR1 = [
          'Box of Joe',
          'CA12DE',
          '12345'
        ];
searchkey "CA12DE" exists in the hash...
[download]