#!/usr/bin/perl
use warnings;
use strict;

# Untermuster, Groß-/Kleinschreibung nicht unterschieden
my $submuster = qr/(?i)[1-8pbnrqk]+/;

# Testdaten - nur der erste String ist korrekt!
for my $string (<DATA>) {
    chomp $string;
    if($string =~ m!^(?:$submuster/){7}$submuster [wb] [-KkQq] [-a-h36]+$!) {
        print "$string: ja";
    } else {
        print "$string: nein";
    }
    print "\n";
}
__DATA__
2B3K1/8/3N1p1p/6pk/5P1P/6P1/7r/5r2 w - -
 2/8/Np/6pk/5P1P/6P1/7r/5r2 w - -
/2B3K1/8/3N1p1p/6pk/5P1P/6P1/7r/5r2 w - -
2B3Y1/8/3N1p1p/6pk/5P1P/6P1/7r/5r2 w - -
2B3K1/8/3N1p1p/6pk/5P1P/6P1/7r/5r2 W - -
2B3K1/8/3N1p1p/6pk/5P1P/6P1/7r/5r2 - -
2B3K1/8/3N1p1p/5P1P/6P1/7r/5r2 w - -
2B3K1/8/8/3N1p1p/6pk/5P1P/6P1/7r/5r2 w - -
2B3K1/8/8/8/3N1p1p/6pk/5P1P/6P1/7r/5r2 w - -