#!/usr/bin/perl
use LWP::UserAgent;
use HTTP::Request::Common qw(GET);
use HTML::Parser;

$UA   = LWP::UserAgent->new();
$req  = HTTP::Request->new( GET => "http://www.example.com/" );
$resp = $UA->request($req);

sub viewstate_finder {
    my ( $self, $tag, $attr ) = @_;

    if ( $attr->{name} eq "__VIEWSTATE" ) {
        $main::viewstate = $attr->{value};
    }
}

my $p = HTML::Parser->new(
    api_version => 3,
    start_h     => [ \&viewstate_finder, "self,tagname,attr" ],
    report_tags => [qw(input)]
);
$p->parse( $resp->content );
$p->eof;

print $main::viewstate . "\n" if $main::viewstate;