gistfile1.pl

use strict;
use HTML::FormHandler;

my $form = HTML::FormHandler->new(
    field_list => {
        fields => [
            foo => { type => 'Text', required => 1 }
        ]
    }
);

if (! $form->process( params => { bar => 1 } )) {
    foreach my $field ($form->error_fields) {
        foreach my $error ($field->errors) {
            warn $error;
        }
    }
}