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use Getopt::Long;
use Pod::Usage;
...
    how to handle option dependencies for most-likely cases.

=cut

( defined($opt{U}) xor defined($opt{H}) )
  || do { print "Only one of 'hostname' or 'uri' must be specified\n";
...
  || do { print "Hostname option requires port option\n";
          pod2usage(1);
        };