For a more Perl-ish version, try something like this...

use Cwd ;
my $curr_dir = cwd ;

opendir DIR , $curr_dir ;
for my $DIR ( grep { /^[a-k]/ || /^lts$/ || /^mon$/ || /^[n-z]/ }
              readdir( DIR )
            )
{
    if ( -d "$DIR/bld" )
    {
        chdir "$DIR/bld" ;
        system 'cbsfpfg.exe', ( 'cbs' . $DIR . $RELEASE ), $DIR ;
        chdir $curr_dir ;
    }
}
closedir DIR ;
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Those who know that they are profound strive for clarity. Those who
would like to seem profound to the crowd strive for obscurity.
            --Friedrich Nietzsche