sub get_ticket
{ 
    my ($rest_client, $sdn_controller) = @_; 
    my $ticket;

    ...

    die "\$ticket undefined in get_ticket()" unless defined $ticket;

    return $ticket;
}

##</code><code>##

MAIN:
{
    my $result = 0;       # normal termination

    eval
    {
        ...               # main code goes here
    }

    $result = 1 if $@;    # abnormal termination

    exit $result;
}