I have attempted to correct it - and this code should get you the expected "submit=a1" in the querystring on hitting "submit".

Also - naming your sub "header" in a CGI program is a bad idea. I changed it to MyHeader.

uuse strict;
use warnings;
use DBI;
use Getopt::Long;
use CGI qw/:all :cgi-lib/;
my  $CGI_params = Vars();
my %CGI_PARAM  = %$CGI_params;
my $site = "";
my $site_selected="a1";
$site = "a1";
$site_selected = $CGI_PARAM{'popup'};
$site = $CGI_PARAM{'popup'};

if($site_selected =~ /^\s*$/) {
    $site = "a1";
    $site_selected="a1";
}
defined $site or die "usage:$0";
my %map=(a1=>[qw(r_a1_c)],a1=>[qw(r_a2_c)],);
show();
sub show{
  status();
  MyHeader();
}
sub status{
my $stm=$site_selected;
}
sub MyHeader
{
print start_form(-method=>"GET",-action=>"db.cgi");
print " <br> &nbsp<B>Site</B> &nbsp";
print popup_menu(
       -name    => 'popup',
       -value  =>  keys % map,
       -default => 'value2'
         );

print "&nbsp &nbsp &nbsp &nbsp &nbsp";
print submit(-type=>"submit",-name=>"submit",-value=>$site);
print end_form, "\n";
}
[download]

[Tue Apr 11 00:18:43.320396 2017] [cgi:error] [pid 32529] [client 192.
+168.231.211:3555] malformed header from script 'db.cgi': Bad header: 
+<form method="get" action="db.
[download]

print header();

Do you realize this is his 4th userid Re: How to use perl mysql query to fetch the maximum of records?,

he has had this all pointed out to him before Re: submit button fails to pass the values using perl cgi?,

and he wont listen to you no matter what you say or do? Re^3: Unable to use if condition inside foreach loop using perl?
- since he just wants to show his power to be able to beg a guru for help Re^6: Unable to use if condition inside foreach loop using perl? (guru system)

And he doesnt even beg well

At least this time he showed where $CGI_PARAM came from

Edit: Interesting nick name The total number of class rooms in GPS.SANA COMPOUND is 1.

Interesting psychological condition discussed in those links.

Thank you for the education on a new kind of troll.

        ...it is unhealthy to remain near things that are in the process of blowing up.     man page for WARP, by Larry Wall

... this is his 4th userid ... he has had this all pointed out to him before ... Interesting nick name The total number of class rooms in GPS.SANA COMPOUND is 1.

Suddenly many things become clear. It is not he but they who are registering all these user names and asking the same questions over and over again.

As is often the case, answers engender more questions. Despite being in a very small school (from the link: thirty-nine students, two teachers, one classroom, four blackboards, no computers — which I take to mean that each student has his or her own laptop), they seem not to share info among themselves. Is this an indication of dedication to individual effort or of unwillingness to cooperate with and support their fellow students?

---

Give a man a fish:  <%-{-{-{-<

the thing is -value=>$site should pass all 'popup'values.

Add this line to top of your script and then fix the errrors

use CGI::Carp 'fatalsToBrowser';
[download]

the thing is -value=>$site should pass all 'popup'values.

The thing should make sense, test, check, its basic debugging

Friend of yours ? submit button fails to pass the values using perl cgi?