use strict;
use Getopt::Long;

my $result = GetOptions (
          "c=s" => \&COMP1,
          "t=s" => \&COMP2, # COMP2 will not be called if option c is null?
          '<>' => sub {print "\nThat is not a valid parameter\n";},
	);

sub COMP1 {print "\nOption -$_[0] is value=$_[1]\n";}
sub COMP2 {print "\nOption -$_[0] is value=$_[1]\n";}

##</code><code>##

use strict;
use Getopt::Long;

my $COMP1 = 0;
my $COMP2 = 0;
my $result = GetOptions (
          "c=s" => \$COMP1,
          "t=s" => \$COMP2,
          '<>' => sub {print "\nThat is not a valid parameter\n";},
	);

if (!$COMP1) {
   if ($COMP2) {
   	print "\nOption t won't run without option C";
  }
}