you need: 
use HTTP::Request::Common qw(POST)

[download]
because you will be posting to the webserver. POST takes a URL and an array ref which it turns into a query string: 
POST $url, [ data => `cat binary_file.dat`,
             user => jimbo,
             pass => heehaw
            ];

[download]

In reply to Re: Using Libwww for a Form Data Upload by princepawn
in thread Using Libwww for a Form Data Upload by Anonymous Monk

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