The optional "$number" parameter is used to distinguish
   between two fields with the same name.  The fields are
   numbered from 1.

use strict;
use warnings;
use CGI qw(:standard);

print header, start_form,
   'Enter something: ', textfield('text1'),
   checkbox_group(
      -name   => 'checkbox1',
      -values => [qw(foo bar baz qux)],
   ), 
   submit('go'), end_form,
;

if (param('go')) {
   print pre(map "$_: @{[param($_)]} \n", param);
}
[download]

use strict;
use warnings;
use WWW::Mechanize;

my $agent = WWW::Mechanize->new();
$agent->get('http://localhost/cgi-bin/foo.cgi');
$agent->form(1);
$agent->field(qw(text1 HELO));
$agent->field(qw(checkbox1 foo 1));
$agent->field(qw(checkbox1 baz 3));
$agent->click('go');

print ($agent->{content} =~ /<pre>(.*)<\/pre>/s);
[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)