You had a "head" conflict between LWP::Simple and CGI. From the documentation:

Note that if you are using both LWP::Simple and the very popular CGI.pm module, you may be importing a head function from each module, producing a warning like:

"Prototype mismatch: sub main::head ($) vs none"
[download]

Get around this problem by just not importing LWP::Simple's head function, like so:

  
use LWP::Simple qw(!head);
use CGI qw(:standard);    # then only CGI.pm defines a head
[download]

Then if you do need LWP::Simple's head function, you can just call it as:

LWP::Simple::head($url)
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I ran your script like this:

#!/usr/bin/perl 

use strict;
use warnings;
use LWP::Simple qw(!head);
use CGI qw/:standard/;
use CGI::Carp qw(fatalsToBrowser);
head();

print header, start_html("test");
my $url    = 'http://www.perlmonks.net';
my $geturl = url_param('geturl');
my $commentid;

if ( defined( $_ = $geturl ) ) {
    &get_url;
}
else {
    &get_site;
    &print_form;

}

sub get_url {
    print qq(<form name="geturl" name="geturl" method="get" action="wp
+.pl">);
    print qq(URL: <input type="text" name="geturl">);
    print qq(<input type="submit" name="submiturl"></form>);
}

sub print_form {
    print "test 1";
}

sub get_site {
    my $content = get($geturl);
    print "test\n";
}
[download]

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