my @strings = ('Hallo K', 'Hallo Karl');
for (@strings) {
    print "$_ : ", teste_string($_), "\n";
}

sub teste_string {
    my ($string) = @_;
    my $ok = 1;
    for (split /\s+/, $string) {
        $ok = 0 unless /\b([a-zA-Z0-9]{2,50})\b/;
    }
    return $ok;
}