As mentioned before:
There are the LWP::UserAgent and HTTP::Request modules, which together allow you to make POST requests.
Example:

use strict;
use HTTP::Request::Common qw(POST);

my $url = 'http://www.somewhere.com/cgi-bin/formular.cgi';

my $req = POST $url,
      [ Host            => 'myHost',
        Server          => 'Any Value',
        OtherField      => 'Some Value',
        OneMoreField    => 'whatever',
      ];


# Just a debug to STDOUT    
print "HTTP-FullRequest-Header: \n";
print $req->headers->as_string() , "\n";

print "HTTP-FullRequest-Header-Content: \n";
print $req->content() ,"\n";



# Now send it
use LWP::UserAgent;

my $ua = LWP::UserAgent->new();

my $response = $ua->request($req);

if ( $response->is_error() ) {
        print "Error-Code    : ", $response->code() ,    "\n";
        print "Error-Message : ", $response->message() , "\n";
}
else {
        print $response->content() , "\n";
}
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HTH