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Often times you'll want to have app-specific helper/utility methods that don't fit neatly in M V or C. The frameworks have various ways of helping you with this:

Examples By Framework

Catalyst

Catalyst can load helper methods in the Controller's auto method. Simply use the Root controller for app-wide methods and the specific Controller for controller-specific methods.

In the app-wide controller: myapp/lib/MyApp/Controller/Root.pm

package MyApp::Controller::Root;

sub auto : Private {
    my ($self, $c) = @_;
    $c->stash->{fmt_currency} = sub { sprintf('%s%0.2f', @_); }
}

1;

In the template: myapp/templates/products.tt

[%- FOREACH product=products -%]
    <tr>
        <td>[% product.name %]</td>
        <td>[% fmt_currency('$',product.unit_price) %]</td>
    </tr>
[%- END -%]

Ruby on Rails

Rails has the concept of a helper module to store these methods. Simply create a module under app/helpers. When the right name is used, the module is automatically loaded and the methods are globally available in your view. For controller-specific methods, use app/helpers/<controller_name>_helper.rb and for app-wide helpers use app/helpers/application_helper.rb.

In the app-wide helper: app/helpers/application_helper.rb

module ApplicationHelper

    def fmt_currency(symbol, amt)
        sprintf("%s%0.2f", symbol, amt)
    end

end

In the template: app/view/products.rhtml

<% for product in @products -%>
    <tr>
        <td><%= product.name %></td>
        <td><%= fmt_currency('$',product.unit_price)</td>
    </tr>
<% end -%>