Hello alwynpan, and welcome to the Monastery!

I’ve never used Catalyst, but looking through the documentation I found this in Catalyst::Manual::Tutorial::02_CatalystBasics:

sub index :Path :Args(0) {
    my ( $self, $c ) = @_;
 
    # Hello World
    $c->response->body( $c->welcome_message );
}
[download]

...

The "$c" here refers to the Catalyst context, which is used to access the Catalyst application. In addition to many other things, the Catalyst context provides access to "response" and "request" objects. (See Catalyst::Runtime, Catalyst::Response, and Catalyst::Request)

No doubt the other monks will be able to provide a fuller explanation. In the meantime, hope that helps,

Hi Athanasius, Thank you for your help. You are correct, it is actually explained in a later section of the document on CPAN. I found the intro document for Catalyst was not quite well organized as it introduced many new things without any explanation or reference. And the explanation was provided in a later chapter which makes the beginners (at least myself) quite lost. Regards, Alwyn

If this is your second day in the Perl world, I would suggest that trying to work with the Catalyst framework is probably premature. I think that you should nail down the basics of Perl before going into Catalyst or any other similar large-scale framework. Otherwise, you're going to make the learning curve much steeper than it needs to be.

IMHO, you should grab a good tutorial or introductory book on Perl (e.g. Learning Perl), get a good understanding on the basic concepts and syntax, spend a couple of weeks on that, and come back to Catalyst afterwards.

Update: fixed a typo: s/leaning/learning/;

In the quoted code,  $c is a lexical (or my) variable initialized from the second item of the argument list of the  hello() and  end() functions — actually, from the code it seems more appropriate to call them "methods" rather than functions. Again from the context of the code, I'd guess the  $c variable in both cases is an object reference. (Update: Please see perlobj.)

The precise name is not important. It could as well have been  $xyzzy or  $some_name_that_has_meaning_for_me just as long as the naming was consistent throughout the function/method.

$c is standard shorthand for the application context in Catalyst. As AnomalousMonk said, the actual variable name is arbitrary, just as $self is but it's also a convention. In the case of your sample code, $self is the Controller object.

During a regular request cycle, in which all controllers participate, $c will have $c->request loaded and you can start writing a $c->response if you like (they both have shorthand too, $c->req and $c->res). In cases where the request has not been processed, like the base class of any Catalyst application or in pre-request configuration code, this convention is often used to disambiguate from the request cycle context: $ctx.

And I think you can start to see why Laurent_R's and my cautions about Catalyst as a first trip to Perlland are good advice. The journey will probably be more torturous than edifying. You have to know HTTP and Perl pretty well, including object oriented Perl, before you can even absorb the answers you'll get to your questions. And you haven't hit Models in Catalyst yet. Almost all the examples in the docs and most real apps use DBIx::Class which also has a steep and dissimilar learning curve.

Don't get me wrong. Catalyst is fantastic; as is DBIC. It's just not starter fare.