use LWP::UserAgent;
use HTTP::Request::Common;
use Digest::MD5::File qw(file_md5_hex);
use File::Slurp;

#text file to upload
my $text_file = 'file.txt';

#calulate Content-MD5 Header
my $md5hash = file_md5_hex($text_file);

#read file
my $file_contents = read_file($text_file);

#fields to post
my %post_parameters = (
	'a' => 'red',
	'b' => 'blue',
	'c' => 'green'
);

$ua = LWP::UserAgent->new();
$ua->agent('Blah/Perl');
$req = new HTTP::Request 'POST','http://amazonmws.blah';
$req->content_type('text/xml; charset=iso-8859-1');
$req->header( 'Content-MD5' => $md5hash );
$req->content([%post_parameters]);
$req->add_content($file_contents);

$res = $ua->request($req);