for  my $x ("\\\\files\\builds\\data\\M9998SBQCACSYD30401S", "\\\\files\\builds\\data\\M9998SBQCACSAD30401S") {
    if($x =~ /Y[A-Z]\d+[^\d\\]*$/) {
		print "$x matches\n";
	} else {
		print "$x doesn't match\n";
    }
}