A.18 Chapter 19, CGI Programming

1. Here's one way to do it:

   use strict;
   use CGI qw(:standard);
   
   print header(), start_html("Add Me");
   print h1("Add Me");
   if(param()) {
       my $n1 = param('field1');
       my $n2 = param('field2');
       my $n3 = $n2 + $n1;
       print p("$n1 + $n2 = <strong>$n3</strong>\n");
   } else {
       print hr(), start_form();
       print p("First Number:", textfield("field1"));
       print p("Second Number:", textfield("field2"));
       print p(submit("add"), reset("clear"));
       print end_form(), hr();
   }
   print end_html();

   If there's no input, simply generate a form with two textfields (using the textfield method). If there is input, we add the two fields together and print the result.

2. Here's one way to do it:

   use strict;
   use CGI qw(:standard);
   
   print header(), start_html("Browser Detective");
   print h1("Browser Detective"), hr();
   my $browser = $ENV{'HTTP_USER_AGENT'};
   $_ = $browser;
   
   BROWSER:{
       if (/msie/i) {
               msie($_);
       } elsif (/mozilla/i) {
               netscape($_);
       } elsif (/lynx/i) {
               lynx($_);
       } else {
               default($_);
       }
   }
   
   print end_html();
   sub msie{ 
       print p("Internet Explorer: @_.  Good Choice\n");
   }
   
   sub netscape {
       print p("Netscape: @_.  Good Choice\n");
   }
   
   sub lynx {
       print p("Lynx: @_.  Shudder...");
   }
   
   sub default {
       print p("What the heck is a @_?");
   }

   The key here is checking the environment for the HTTP_USER_AGENT variable. Although this isn't implemented by every server, many of them do set it. This is a good way to generate content geared to the features of a particular browser. Note that we're just doing some basic string matching (case insensitive) to see what they're using (nothing too fancy).