Ideally, you'd give checkboxes different names:
(Using a travel agent site as an example.)

# <input type="checkbox" name="search_first_class">
# <input type="checkbox" name="search_economy_class">

my $search_first_class   = $cgi->param('search_first_class');
my $search_economy_class = $cgi->param('search_economy_class');

warn("Classes to search:"
   . ($search_first_class   ? ' First'   : '')
   . ($search_economy_class ? ' Economy' : '')
) if $DEBUG;
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But you can give them the same name if they have different values:

# <input type="checkbox" name="search_class" value="first">
# <input type="checkbox" name="search_class" value="economy">

# Call $cgi->param in a list context.
my @search_classes = $cgi->param('search_class');

warn("Classes to search: " . join(' ', @search_classes))
   if $DEBUG;

# # The array can be converted to a hash for easy to lookup.
# my %search_classes;
# @search_classes{@search_classes} = @search_classes;
#
# warn("Classes to search:"
#    . ($search_class{'first'  } ? ' First'   : '')
#    . ($search_class{'economy'} ? ' Economy' : '')
# ) if $DEBUG;
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Update: I concur with Ovid. The second case is the ideal one, not the first. What was I thinking??