Actually ... i would desire this:

use strict;
use warnings;

my $arg   = shift || 'boo';
my @valid = qw( goo moo foo voo doo poo );

print "$arg matches\n" if grep /$arg/, @valid;
[download]

But this bring up an annoyance as well, because this mistake will compile and always return true (as long as the array being checked is not empty):

# wrong way ahead!
print "$arg matches\n" if grep $arg, @valid;
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)