Apache: The Definitive Guide, 3rd Edition

Getting Data from the Client

On many sites in real life, we need to ask the visitor what he wants, get the information back to the server, and then do something with it. This, after all, is the main mechanism of e-commerce. HTML provides one standard method for getting data from the client: the Form. If we use the HTML Method='POST' in the form specification, the data the user types into the fields of the form is available to our script by reading stdin.

In POST-based Perl CGI scripts, this data can be read into a variable by setting it equal to <>:

my ($data);
$data=<>;

We can then rummage about in $data to extract the values type in by the user.

In real life, you would probably use the CGI module, downloaded from CPAN (http://cpan.org), to handle the interface between your script and data from the form. It is easier and much more secure than doing it yourself, but we ignore it here because we want to illustrate the basic principles of what is happening.

We will add some code to the script to ask questions. One question will ask the reader to click if they want to see a printout of everyone in the database. The other will let them enter a name to replace “Anne” as the search criterion listed earlier.

It makes sense to use the same script to create the page that asks for input and then to handle that input once it arrives. The trick is to test the input channels for data at the top of the script. If there is none, it asks questions; if there is some, it gives answers.