for my $bn ( @B_CHECKS ) {
   my $re = qr/^(?:0|5|6)0+\Q$bn\E$/;
   for my $cn ( @CS_CHECKS ) {
      if ( $cn =~ $re ) {
         print "$bn = $cn\n";
      }
   }
}

##</code><code>##

my ($re) = map qr/^(?:0|5|6)0+($_)$/,
           join '|',
           map quotemeta,
           @B_CHECKS;

for my $cn ( @CS_CHECKS ) {
   if ( $cn =~ $re ) {
      print "$1 = $cn\n";
   }
}

##</code><code>##

use Regexp::List qw( ) 

my $re = Regexp::List->new->list2re(@B_CHECKS);
$re = qr/^(?:0|5|6)0+($re)$/;
for my $cn ( @CS_CHECKS ) {
   if ( $cn =~ $re ) {
      print "$1 = $cn\n";
   }
}

##</code><code>##

my %B_CHECKS = map +($_ => 1), @B_CHECKS;
for my $cn ( @CS_CHECKS ) {
   (my $bn = $cn) =~ s/^(?:0|5|6)0+//;
   if ( $B_CHECKS{$bn} ) {
      print "$bn = $cn\n";
   }
}