Must it be an array? I've had good luck with the transliteration operator:

my $good = "abcde";
my $bad = "zyxwv";
my $mixed = "azby";

for ($good, $bad, $mixed) {
    print "$_ contains invalid characters!\n" if tr/a-m//c;
}
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Yes, this approach has some limitations, the most severe being that tr/// doesn't perform variable interpolation. It's still nice to know.