Catalyst - The Elegant MVC Web Application Framework


    # use the helper to start a new application MyApp

    # add models, views, controllers
    script/ model Database DBIC dbi:SQLite:/path/to/db
    script/ view TT TT
    script/ controller Search

    # built in testserver -- use -r to restart automatically on changes

    # command line testing interface
    script/ /yada

    ### in
    use Catalyst qw/-Debug/; # include plugins here as well
    sub foo : Global { # called for /foo, /foo/1, /foo/1/2, etc.
        my ( $self, $c, @args ) = @_; # args are qw/1 2/ for /foo/1/2
        $c->stash->{template} = ''; # set the template
        # lookup something from db -- stash vars are passed to TT
        $c->stash->{data} = 
          MyApp::Model::Database::Foo->search( { country => $args[0] } );
        if ( $c->req->params->{bar} ) { # access GET or POST parameters
            $c->forward( 'bar' ); # process another action
            # do something else after forward returns            
    # The TT template can use the stash data from the database
    [% WHILE (item = %]
        [% %]
    [% END %]
    # called for /bar/of/soap, /bar/of/soap/10, etc.
    sub bar : Path('/bar/of/soap') { ... }

    # called for all actions, from the top-most controller downwards
    sub auto : Private { 
        my ( $self, $c ) = @_;
        if ( !$c->user ) {
            $c->res->redirect( '/login' ); # require login
            return 0; # abort request and go immediately to end()
        return 1; # success; carry on to next action
    # called after all actions are finished
    sub end : Private { 
        my ( $self, $c ) = @_;
        if ( scalar @{ $c->error } ) { ... } # handle errors
        return if $c->res->body; # already have a response
        $c->forward( 'MyApp::View::TT' ); # render template

    ### in MyApp/Controller/
    # called for /foo/bar
    sub bar : Local { ... }
    # called for /blargle
    sub blargle : Global { ... }
    # an index action matches /foo, but not /foo/1, etc.
    sub index : Private { ... }
    ### in MyApp/Controller/Foo/
    # called for /foo/bar/baz
    sub baz : Local { ... }
    # first MyApp auto is called, then Foo auto, then this
    sub auto : Private { ... }
    # powerful regular expression paths are also possible
    sub details : Regex('^product/(\w+)/details$') {
        my ( $self, $c ) = @_;
        # extract the (\w+) from the URI
        my $product = $c->req->snippets->[0];

See Catalyst::Manual::Intro for additional information.


The key concept of Catalyst is DRY (Don't Repeat Yourself).

See Catalyst::Manual for more documentation.

Catalyst plugins can be loaded by naming them as arguments to the "use Catalyst" statement. Omit the Catalyst::Plugin:: prefix from the plugin name, i.e., Catalyst::Plugin::My::Module becomes My::Module.

    use Catalyst qw/My::Module/;

Special flags like -Debug and -Engine can also be specified as arguments when Catalyst is loaded:

    use Catalyst qw/-Debug My::Module/;

The position of plugins and flags in the chain is important, because they are loaded in exactly the order in which they appear.

The following flags are supported:


Enables debug output.


Forces Catalyst to use a specific engine. Omit the Catalyst::Engine:: prefix of the engine name, i.e.:

    use Catalyst qw/-Engine=CGI/;


Forces Catalyst to use a specific home directory, e.g.:

    use Catalyst qw[-Home=/usr/sri];


Specifies log level.


Information about the current request


Returns a Catalyst::Action object for the current action, which stringifies to the action name. See Catalyst::Action.


Returns the namespace of the current action, i.e., the uri prefix corresponding to the controller of the current action. For example:

    # in Controller::Foo::Bar
    $c->namespace; # returns 'foo/bar';



Returns the current Catalyst::Request object. See Catalyst::Request.

Processing and response to the current request

$c->forward( $action [, \@arguments ] )

$c->forward( $class, $method, [, \@arguments ] )

Forwards processing to a private action. If you give a class name but no method, process() is called. You may also optionally pass arguments in an arrayref. The action will receive the arguments in @_ and $c->req->args. Upon returning from the function, $c->req->args will be restored to the previous values.

Any data returned from the action forwarded to, will be returned by the call to forward.

    my $foodata = $c->forward('/foo');
    $c->forward(qw/MyApp::Model::CDBI::Foo do_stuff/);

$c->detach( $action [, \@arguments ] )

$c->detach( $class, $method, [, \@arguments ] )

The same as forward, but doesn't return.


$c->error($error, ...)


Returns an arrayref containing error messages. If Catalyst encounters an error while processing a request, it stores the error in $c->error. This method should not be used to store non-fatal error messages.

    my @error = @{ $c->error };

Add a new error.

    $c->error('Something bad happened');

Clear errors. You probably don't want to clear the errors unless you are implementing a custom error screen.




Returns the current Catalyst::Response object.


Returns a hashref to the stash, which may be used to store data and pass it between components during a request. You can also set hash keys by passing arguments. The stash is automatically sent to the view. The stash is cleared at the end of a request; it cannot be used for persistent storage.

    $c->stash->{foo} = $bar;
    $c->stash( { moose => 'majestic', qux => 0 } );
    $c->stash( bar => 1, gorch => 2 ); # equivalent to passing a hashref
    # stash is automatically passed to the view for use in a template
    $c->forward( 'MyApp::V::TT' );


Contains the return value of the last executed action.

Component Accessors



Gets a component object by name. This method is no longer recommended, unless you want to get a specific component by full class. $c->controller, $c->model, and $c->view should be used instead.


Gets a Catalyst::Controller instance by name.



Gets a Catalyst::Model instance by name.



Gets a Catalyst::View instance by name.


Class data and helper classes


Returns or takes a hashref containing the application's configuration.

    __PACKAGE__->config({ db => 'dsn:SQLite:foo.db' });

You can also use a YAML config file like myapp.yml in your applications home directory.

    db: dsn:SQLite:foo.db


Overload to enable debug messages (same as -Debug option).


Returns the dispatcher instance. Stringifies to class name. See Catalyst::Dispatcher.


Returns the engine instance. Stringifies to the class name. See Catalyst::Engine.


Returns the logging object instance. Unless it is already set, Catalyst sets this up with a Catalyst::Log object. To use your own log class, set the logger with the __PACKAGE__->log method prior to calling __PACKAGE__->setup.

 __PACKAGE__->log( MyLogger->new );

And later:

    $c->log->info( 'Now logging with my own logger!' );

Your log class should implement the methods described in the Catalyst::Log man page.

Utility methods


Merges @path with $c->config->{home} and returns a Path::Class object.

For example:

    $c->path_to( 'db', 'sqlite.db' );

$c->plugin( $name, $class, @args )

Helper method for plugins. It creates a classdata accessor/mutator and loads and instantiates the given class.

    MyApp->plugin( 'prototype', 'HTML::Prototype' );



Initializes the dispatcher and engine, loads any plugins, and loads the model, view, and controller components. You may also specify an array of plugins to load here, if you choose to not load them in the use Catalyst line.

    MyApp->setup( qw/-Debug/ );

$c->uri_for( $path, [ @args ] )

Merges path with $c->request->base for absolute uri's and with $c->namespace for relative uri's, then returns a normalized URI object. If any args are passed, they are added at the end of the path.


Returns the Catalyst welcome HTML page.


These methods are not meant to be used by end users.


Returns a hash of components.


Returns or sets the context class.


Returns a hashref containing coderefs and execution counts (needed for deep recursion detection).


Returns the number of actions on the current internal execution stack.


Dispatches a request to actions.


Returns or sets the dispatcher class.


Returns a list of 2-element array references (name, structure) pairs that will be dumped on the error page in debug mode.


Returns or sets the engine class.

$c->execute( $class, $coderef )

Execute a coderef in given class and catch exceptions. Errors are available via $c->error.


Finalizes the request.


Finalizes body.


Finalizes cookies.


Finalizes error.


Finalizes headers.


An alias for finalize_body.


Finalizes the input after reading is complete.


Finalizes uploads. Cleans up any temporary files.

$c->get_action( $action, $namespace )

Gets an action in a given namespace.

$c->get_actions( $action, $namespace )

Gets all actions of a given name in a namespace and all parent namespaces.

handle_request( $class, @arguments )

Called to handle each HTTP request.

$c->prepare( @arguments )

Creates a Catalyst context from an engine-specific request (Apache, CGI, etc.).


Prepares action.


Prepares message body.

$c->prepare_body_chunk( $chunk )

Prepares a chunk of data before sending it to HTTP::Body.


Prepares body parameters.


Prepares connection.


Prepares cookies.


Prepares headers.


Prepares parameters.


Prepares path and base.


Prepares query parameters.


Prepares the input for reading.


Prepares the engine request.


Prepares uploads.


Prepares the output for writing.


Returns or sets the request class.


Returns or sets the response class.

$c->read( [$maxlength] )

Reads a chunk of data from the request body. This method is designed to be used in a while loop, reading $maxlength bytes on every call. $maxlength defaults to the size of the request if not specified.

You have to set MyApp->config->{parse_on_demand} to use this directly.


Starts the engine.

$c->set_action( $action, $code, $namespace, $attrs )

Sets an action in a given namespace.


Sets up actions for a component.


Sets up components.


Sets up dispatcher.


Sets up engine.


Sets up the home directory.


Sets up log.


Sets up plugins.


Returns the stack.

$c->write( $data )

Writes $data to the output stream. When using this method directly, you will need to manually set the Content-Length header to the length of your output data, if known.


Returns the Catalyst version number. Mostly useful for "powered by" messages in template systems.


Catalyst uses internal actions like _DISPATCH, _BEGIN, _AUTO, _ACTION, and _END. These are by default not shown in the private action table, but you can make them visible with a config parameter.

    MyApp->config->{show_internal_actions} = 1;


By default Catalyst is not case sensitive, so MyApp::C::FOO::Bar is mapped to /foo/bar. You can activate case sensitivity with a config parameter.

    MyApp->config->{case_sensitive} = 1;

This causes MyApp::C::Foo::Bar to map to /Foo/Bar.


The request body is usually parsed at the beginning of a request, but if you want to handle input yourself or speed things up a bit, you can enable on-demand parsing with a config parameter.

    MyApp->config->{parse_on_demand} = 1;


Many production servers operate using the common double-server approach, with a lightweight frontend web server passing requests to a larger backend server. An application running on the backend server must deal with two problems: the remote user always appears to be and the server's hostname will appear to be localhost regardless of the virtual host that the user connected through.

Catalyst will automatically detect this situation when you are running the frontend and backend servers on the same machine. The following changes are made to the request.

    $c->req->address is set to the user's real IP address, as read from 
    the HTTP X-Forwarded-For header.
    The host value for $c->req->base and $c->req->uri is set to the real
    host, as read from the HTTP X-Forwarded-Host header.

Obviously, your web server must support these headers for this to work.

In a more complex server farm environment where you may have your frontend proxy server(s) on different machines, you will need to set a configuration option to tell Catalyst to read the proxied data from the headers.

    MyApp->config->{using_frontend_proxy} = 1;

If you do not wish to use the proxy support at all, you may set:

    MyApp->config->{ignore_frontend_proxy} = 1;


Catalyst has been tested under Apache 2's threading mpm_worker, mpm_winnt, and the standalone forking HTTP server on Windows. We believe the Catalyst core to be thread-safe.

If you plan to operate in a threaded environment, remember that all other modules you are using must also be thread-safe. Some modules, most notably DBD::SQLite, are not thread-safe.



    Join #catalyst on

Mailing Lists:




Task::Catalyst - All you need to start with Catalyst

Catalyst::Manual - The Catalyst Manual

Catalyst::Component, Catalyst::Base - Base classes for components

Catalyst::Engine - Core engine

Catalyst::Log - Log class.

Catalyst::Request - Request object

Catalyst::Response - Response object

Catalyst::Test - The test suite.


Andy Grundman

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This library is free software, you can redistribute it and/or modify it under the same terms as Perl itself.