sub Main {
    my %CONFIG;
    initialize_config_hash(\%CONFIG);
    get_command_line_args(\%CONFIG);
    validate_command_line_args(\%CONFIG);
    get_username_and_password_from_stdin(\%CONFIG) if $CONFIG{prompt};
    
    ...
}

sub initialize_config_hash {
    my $CONFIG = shift;
    %$CONFIG = (
        quiet          => 0      , cfg       => "$name.cfg"         ,
        verbose        => 0      , outcsv    => "$name.csv"         ,
        debug          => 0      , proto     => "none"              ,
        prompt         => 1      , header    => undef               ,
        layout         => 0      , maildst   => []                  ,
        wait_for_child => 120    , mail_to   => ""                  ,
        wait_for_exec  => 0      , mail_from => "NMS-script@me.net" ,
        batchsize      => 0      , mail_sub  => ""                  ,
        tacacs         => 0      , mail_cc   => ""                  ,
        tacuser        => "user" , mail_data => ""                  ,
        tacpass        => "pass" ,
    );
}

sub get_command_line_args {
    my $CONFIG = shift;
    GetOptions (
        'layout|l'            => \$CONFIG->{layout},
        'file-based-auth|f'   => sub { \$CONFIG->{prompt} = 0; },
        'prompt-based-auth|p' => sub { \$CONFIG->{prompt} = 1; },
        ...
    )
    ...
}