Chapter 11

Instance Parameters

Every CGI::Application needs at least two pieces a module containing a subclass 

of CGI::Application and an instance script that uses that module. The example 

instance script in Listing 11 2 does nothing more than call new() on the BBS class 

and then run() on the returned object:

my $bbs = BBS >new();

$bbs >run();

For simple applications this is all you'll need. However, it is possible to use the 

instance script to modify the behavior of the application.

One way CGI::Application provides configurability is through the TMPL_PATH

option. When your application calls the load_tmpl() method to instantiate an 

HTML::Template object, the filename must be either an absolute path or relative 

to the current directory. But if you specify the TMPL_PATH option to new(), you can 

tell CGI::Application to look elsewhere for your templates. For example, if I wanted 

to keep the templates for the BBS application in /usr/local/templates, I could 

adjust the call to new() to look as follows:

my $bbs = BBS >new(TMPL_PATH => "/usr/local/templates/");

This option could be used to deploy multiple instances of the BBS module with 

different designs coming from different template sets. Each instance script uses 

the same module, but the constructed objects will use different templates, and as 

a result the user will see a different design in his or her browser.

Aside from configuring CGI::Application, new() also includes support for 

application specific parameters. Using the PARAMS option, you can specify a set of 

key value pairs that can be accessed later by the application. For example, imagine 

that the BBS module was written to store its messages in a Berkley DB file accessed 

using the DB_File module. Each instance of the BBS will need its own file to store 

messages. This could be provided using the PARAMS option to new():

my $bbs = BBS >new(PARAMS => { message_db => "/tmp/bbs1.db" });

Now in the BBS code this value can be accessed using the param() method on 

the CGI::Application object:

use DB_File;

sub list {

  my $self = shift;

  my $filename = $self >param( message_db ); # get the configured db filename

  tie %db, "DB_File", $filename;             # access it with DB_File

  # ...

}

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