my @b = map uc, @a;                  # 1 to 1
my @b = map { $_ => uc($_) } @a;     # 1 to N, const ratio
my @b = map { /^#/ ? () : $_ } @a;   # 1 to N

##</code><code>##

print join '|', map uc, qw( a b c );