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my %params=(
  host => (TYPE=>"s", REQUIRED=>1, VALUE=>undef,
...
  password =>  (TYPE=>"s", REQUIRED=>1, VALUE=>undef),

);

GetOptions(
   map { "$_=$params{$_}{TYPE}" => \$params{$_}{VALUE}  } keys %params
...
  showUsage("Missing required parameter $_") if $params{$_}{REQUIRED} 
+&& ! $params{$_}{VALUE};
  $params{$_}{VALIDATE}->($params{$_}{VALUE})  if   $params{$_}{VALIDA
+TE};
}