use 5.010;
use List::MoreUtils qw( sort_by );

my @PCHR = qw( K Q R B N P );
my %pchr = map { $PCHR[$_] => $_ } 0..$#PCHR;
my $w1 = 'QRKPNB';
my $w2 = join '', sort_by { $pchr{$_} } split( //, $w1 );
say "$w1 -> $w2";