I'm a Getopt::Long fan. Rather than using separate variables, I use the option to put all the arguments into a hash. As well, I integrate with documentation using Pod::Usage. Initializing the options hash provides default values. '-help' displays a brief summary, while '-man' displays the full POD.

    my %options = ( date    => prev_day( strftime( '%Y%m%d', localtime
+ )),
                    qadir   => $QADIR,
                    proddir => $PRODDIR,
                  );
    GetOptions( \%options,
                'date=s', 'qadir=s', 'proddir=s', 'exch=s',
                'altexch=s',
                'man', 'help', 'alert!', 'debug+' )
        || pod2usage(2);

    pod2usage(1) if $options{'help'};
    pod2usage( '-verbose' => 2 ) if $options{'man'};
[download]

To handle mandatory arguments, obviously there's no default. Instead, I test for a value. If '-file' has not been provided, I print the message followed by '-help' summary, and exit with status '1'. The only pain is testing all the requirements and inter-correlations between arguments and coming up with the correct set of error messages. It's very irritating to get an error message for a program, provide the requested argument, and get a next error message.

    pod2usage( { -message => q{Mandatory argument '-file' is missing} 
+,
                 -exitval => 1  ,
                 -verbose => 1
               }
             ) unless $options{file};
[download]