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).