# Predeclare which parameters are needed and also specify
 # which are expected to contain lists. All others are
 # expected to contain scalars.
 use constant EXPECTED_PARAMETERS =>
     { sort_preference => '',
       signature       => '',
       display_fields  => 'ARRAY' };

 # Get the CGI object
 my $q = CGI->new;

 # Get the parameters and store in a hash reference
 my $params = get_parameters( $q, EXPECTED_PARAMETERS );

 # Do whatever the script does
 .....

 sub get_parameters {
     # The first parameter is the CGI object.
     # The second parameter is an hash reference
     # to the list of expected parameters. The values
     # are examined for the string 'ARRAY' and those
     # are then retrieved into array references.
     my $q = shift;
     my $expected = shift;

     # Get a list of all the parameter names in a hash
     # This allows me to do exists() tests for parameters
     my %params;
     my @params{ $q -> params } = ();

     # Now go get each expected parameter
     my %extracted;
     while (my ($param_name,
                $param_type) = each %$expected) {
         # warn of missing parameters
         unless (exists $params{$param_name}) {
             cluck "Missing CGI parameter $param_name";
             next;
         }
         
         # Copy the value over. This does a bit of fancy
         # footwork by extracting 'ARRAY' parameters into
         # arrays and all others into a plain scalar. It is
         # not sufficient to simply copy over values since
         # the behaviour for CGI's param() function changes
         # depending on the value of wantarray().
         $extracted{$param_name} =
             $param_type eq 'ARRAY'
             ? [ $q -> param($param_name) ]
             : $q -> param($param_name);

     # Return the expected parameter list as a
     # hash reference.
     return \ %extracted
 }