Note too that you can test your CGI script from the command line passing the CGI parameters on the command line to the script:

#!/usr/bin/perl

use strict;
use warnings;
use CGI qw();

my $na = CGI::param('v1');
my $nb = CGI::param('v2');
my $oper = CGI::param('oper');

print CGI::header();
print "<p>$na $oper $nb</p>\n";
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using a command line of v1=1 v2=2 oper="*" prints:

Content-Type: text/html; charset=ISO-8859-1

<p>1 * 2</p>
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