my $tt = Template->new({
    VARIABLES => {
        version => 3.14,
        release => 'Sahara',
    },  
});

my $vars = {
    serial_no => 271828,
};

$tt->process('myfile', $vars);

##</code><code>##

my $tt = Template->new({
    CONSTANTS => {
        version => 3.14,
        release => 'skyrocket',
        col     => {
            back => '#ffffff',
            fore => '#000000',
        },
        myobj => My::Object->new(),
        mysub => sub { ... },
        joint => ', ',
    },
});

##</code><code>##

my $tt = Template->new({
    CONSTANTS => { current_constants() },
});