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my @upChars = getUpperCaseChars( @chars );
# @upChars is now ( 'A', 'B', 'C', undef, undef, undef, 'F', 'G' )

my @charsWithNoUpperCase =
    @chars[grep { !defined @upChars[$_] } 0..$#upChars];

my @charsWithNoUpperCase
foreach my $index ( 0..$#upChars ) { 
    push @charsWithNoUpperCase, $chars[$index]
        if !defined $upChars[$index];
}