use strict;
use warnings;

use Getopt::Long;

my $prod_type = "";
my $in_file = "";
my $out_file = "";
my $img_file = "";

my $valid = GetOptions(
  'p=s' => \$prod_type,
  'i=s' => \$in_file,
  'o=s' => \$out_file,
  'h=s' => \$img_file,
);


if (($in_file eq "") and ($img_file eq "")) {
  my $msg = "";
  die "Missing required option(s). The -i or -h option must be specified.";
}

if ($in_file ne "") {
  # do some stuff and ignore the -h flag
}
else {
  # do other stuff
  # earlier if statement guarantees that -h flag was used
  #  i.e there was no -i flag used, but the -h flag was used
}