entered in your Web form) or how many bounces you will get when your mailing list system finds thousands of @AOL or user @ aol type of data errors Sanity check user data CGI scripts are often the target of many security attacks If your CGI script accepts user input make sure you validate user data before making use of it

Before you start reinventing the wheel, check the Comprehensive Perl Archive Network (CPAN) site at http://cpanperlcom for existing Perl modules that you can use to solve your current problem or to reduce your development efforts by reusing existing CPAN modules In this section, I use many CPAN modules for building CGI scripts Whenever you see a module listed in any of the scripts discussed here, you can add the module to your system using the CPAN module that is shipped with standard Perl Apache for Windows users should consult Perl documentation for how to use CPAN modules because it differs from the standard approach discussed here See also the Windows-specific section of this book for details

For example, say that you see a script list a module called HTML::Template and would like to install this module so that you can run the script that uses it To install the CPAN module, run perl -MCPAN -e shell from the command prompt as root

If you are running the perl MCPAN e shell command for the first time you will be asked to configure the current CPANpm module, which is used to install other CPAN modules Simply follow the instructions and prompts to configure the CPANpm module and then proceed to the discussion below

After you are at the CPAN prompt, run the install HTML::Template command to install the module The CPAN module will install this module for you If it complains about a dependency, you might have to install some other modules before you can install a module that depends on other CPAN modules After you re done, run quit from the CPAN prompt to return to shell

If you do not want to run the interactive CPAN shell using perl -MCPAN -e shell to install a module, you can run perl -MCPAN -e CPAN::Shell->install (modulename) instead For example, perl -MCPAN -e shell CPAN:: Shell->install(HTML::Template) will install the HTML::Template module You can also run this command from a shell script

CGI scripts are typically used to take user input and perform one or more operations based on the input and return results in a HTML page In this section I show you how to create a simple script to get started and to understand CGI scripting concepts The script that we will develop here will perform a single task: it will take a user s full name, format it properly, and return a personalized greeting message Listing 12-2 shows greetingspl script that does exactly that

#!/usr/bin/perl # # # Name: greetingspl # # Purpose: # # Show a greeting message # ########################################################## use strict; use CGI; # # Get user data # my $query = new CGI; my $name = $query->param( name ); # # Process data # $name = lc($name); my @strArray = (); foreach my $str (split(/ /,$name)) { push(@strArray, ucfirst($str)); } my $formattedName = join( , @strArray); # # Display results # print $query->header; print $query->start_html( Greetings ); print $query->p( Hello $formattedName , ); print $query->p( Thanks for coming to our Web site ); print $query->end_html; # # Terminate # exit 0;

Now, lets take a close look at this script The very first line is a special line:

This line tells the system to run Perl whenever executing this script If you have installed Perl in a non-standard directory, then you must modify this line accordingly For example, if you installed Perl in /usr/local/bin/perl, then you must change this line to reflect that All the lines (other than the very first one) that start with a # sign are a commented out and ignored by Perl The next code segment is:

use strict; use CGI;

The use strict is a Perl pragma (think of pragma as a directive), which tells Perl to evaluate the script for unsafe programming habits The next line tells Perl to load a popular module that is now part of the standard Perl distribution, module called CGIpm, which makes writing CGI programs very easy This modules handles all the underlying details of getting input data that are passed onto the script via STDIN by the Apache server, parsing and decoding input fields, providing methods for displaying content headers, creating HTML contents, and so on It is simply the super -CGI module available to you No one should write CGI scripts in Perl without the CGIpm module The only exception to that rule is if you have a resource constraint and don t want to load a large module each time a script is called But in most cases, this is not an issue, especially since because I do not recommend CGI solutions for high -volume Web sites The next code segment is:

my $query = new CGI; my $name = $query->param( name );

Here a new CGI object called $query is created and the param() method of the $query CGI object is called to get the value for the user input name The value for this input is stored in $name variable For example, if the greetingspl script is called as follows: