You can create a hash with your globals and have Getopt override them if needed.

use Getopt::Long;

sub get_options {
        my $def = shift;
        my $cur = {};
        $cur->{$_->[0]} = $_->[2] for @$def;
        my @def = map {$_->[0].$_->[1]} @$def;
        GetOptions( $cur, @def );
        return $cur;
}

my $defaults = [
    [ debug => '' => 0 ],
    [ help => '' => 0 ],
    [ interactive => '' => 0 ],
    [ host => '=s' => '999.999.999' ],
    [ username => '=s' => 'username' ],
    [ home => '=s' => $ENV{HOME} ],
    # ...
];

my $opt = get_options( $defaults );

# if ( $opt->{help} ) { ... }
# foo( $opt->{host} );
[download]

You loose strict being able to catch your typo's but it becomes real easy to add new options/variables.

Some refactoring wouldn't hurt...

sub debug {
    my $msg = shift;
    writeLog( $msg ) if $opt->{debug};
}
sub timestamp {
    my $when = shift || time;
    my ( $sec, $min, ... ) = localtime( $when );
    # ...
    return $stamp;
}
[download]

You might benefit from placing some of your comments into POD format.

There are places you might be able to do something like:

# ...
my @k = ( 'Status', 'Time Stamp', 'Value', 'Error Message' );
my $h = $HoHoHoA{$line_number_being_processed};
$one_line_summary = $h->{shift(@k)} . 'No Error. ';
$one_line_summary .= $h->{$_} . '. ' for @k;
$one_line_summary .= "$j.";
[download]

In general, when you see lot's of lines that look the same except for one or two differences there's probably a way to clean it up and make it easier to add one more thing without copying a line from above and changing that one different thing.

Just a personal thing, when processing hash keys i usually transform them into all lower case and change whitespace to '_' so i don't have to quote them as often.

my @k = qw/ status time_stamp value error_message /;
[download]

Which just saves a bit of typing here and there.

Otherwise, if it does what you want it to do...