Check out HTTP::Request::Common

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

my $request = POST 'http://www.server.com/script.cgi',
   [
      userid => 'ikegami',
      answer => 'yes indeed',
   ];

print($request->content, "\n");

# Prints:
# userid=ikegami&answer=yes+indeed
[download]

It even uses "+" even though "%20" is equivalent. If your CGI script doesn't handle "+" and "%20", it's broken since you can't tell the browser which way to encode the space.