#PSEUDOCODE

# setting deafult is useful
my $chars = 70; # chars per line
my %display = (name=>'screen');
my $bw; # not monochromo by default

# Getopt::Long part assign command line provided values to $chars and $display{name}
..

# validation and exclusion

my @checks = (
   [\$display{name}, sub{ if ($display{name} eq 'tv'){
                                $chars = 35;
                                $bw = undef;
                          }
                          print "--display tv sets --chars to 35 and clean --monochromo\n" }],

   [\$chars, sub{die "chars 12-140!" if ($chars<12 || $chars>140)} ],

   [\$bw, undef]
);

foreach my $i (0..$#checks){
   if defined the 0th element and also the first one, execute the latter