I am trying to automate web navigation and need to fill a form that has a html text input with a default value

http://genome.ucsc.edu/cgi-bin/hgTables?command=start

this is website

<input type="TEXT" name="position" size="26" value="chr21:33031597-33041570" onfocus="setRadioCheck('hgta_regionType', 'range'); regionType='range'">

but i am unable to change the default value to the text input using set_fields()method.

My code

use WWW::Mechanize;

my $mech = WWW::Mechanize->new();
$mech->agent('Mozilla/5.0');
$mech->proxy(['https', 'http', 'ftp'], 'http://202.41.70.84:6588');
open(DIR,"C:\\Users\\DELL\\Desktop\\Output\\outofBlat.txt") or die "Co
+uldnt open";
open (FH1,">>C:\\Users\\DELL\\Desktop\\outoftables.html");
my@x=<DIR>;
$num=1;

$input="chr21:36259390-36260987";
     
    
$url="http://genome.ucsc.edu/cgi-bin/hgTables?hgsid=304457625";
    
$mech->get($url);

die $mech ->res->status_line unless $mech ->success ;
    
            #+ML::Form
            
    $form = $mech->form_name("mainForm");
            
    foreach my $inputfield (@inputfields) {
            
                                                if ($inputfield=~/posi
+tion/)
                                                {
                                                $mech->set_fields($inp
+utfield=>$input);
                                                }
                                            }

            
$mech->submit;
            
            
die $mech ->res->status_line unless $mech ->success ;

# If the form sends you somewhere, you can catch it :
my $new_url = $mech ->response->request->uri->as_string ;

$html= $mech->content;
                        
            print $html;
            print FH1 $html;


[download]

help me plz ...URGENT