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Author image Alexis Sukrieh




Dancer is a web application framework designed to be as effortless as possible for the developer.

Dancer is here to provide the simpliest way for writing a web application.

It can be use to write light-weight web services or small standalone web applications.

If you don't want to write a CGI by hand and find Catalyst too big for your project, Dancer is what you need.


As soon as Dancer is imported to a script, that script becomes a webapp. All the script has to do is to declare a list of routes. A route handler is composed by an HTTP method, a path pattern and a code block.

The code block given to the route handler has to return a string which will be used as the content to render to the client.

Routes are defined for a given HTTP method. For each method supported, a keyword is exported by the module.

Here is an example of a route definition:

    get '/hello/:name' => sub {
        # do something important here
        return "Hello ".params->{name};

The route is defined for the method 'get', so only GET requests will be honoured by that route.


All existing HTTP methods are defined in the RFC 2616 http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html.

Here are the ones you can use to define your route handlers.

GET The GET method retrieves information (when defining a route handler for the GET method, Dancer automatically defines a route handler for the HEAD method, in order to honour HEAD requests for each of your GET route handlers).
POST The POST method is used to create a ressource on the server.
PUT The PUT method is used to update an existing ressource.


The route action is the code reference declared, it can access parameters through the `params' keyword, which returns an hashref. This hashref is a merge of the route pattern matches and the request params.

Below are all the possible ways to define a route, note that it is not possible to mix them up. Don't expect to have a working application if you mix different kinds of route!


A route pattern can contain one or more tokens (a word prefixed with ':'). Each token found in a route pattern is used as a named-pattern match. Any match will be set in the params hashref.

    get '/hello/:name' => sub {
        "Hey ".params->{name}.", welcome here!";


A route can contain a wildcard (represented by a '*'). Each wildcard match will be returned in an arrayref, accessible via the `splat' keyword.

    get '/download/*.* => sub {
        my ($file, $ext) = splat;
        # do something with $file.$ext here


A route can be defined with a Perl regular expression. The syntax is assumed to be a classic Perl regexp except for the slashes that will be escaped before running the match.

For instance, don't do '\/hello\/(.+)' but rather: '/hello/(.+)'

In order to tell Dancer to consider the route as a real regexp, the route must be defined explicitly with the keyword 'r', like the following:

    get r( '/hello/([\w]+)' ) => sub {
        my ($name) = splat;
        return "Hello $name";


Once the script is ready, you can run the webserver just by running the script. The following options are supported:

--port=XXXX set the port to listen to (default is 3000)
--daemon run the webserver in the background
--help display a detailed help message


An action can choose not to serve the current request and ask Dancer to process the request with the next matching route.

This is done with the pass keyword, like in the following example

    get '/say/:word' => sub {
        pass if (params->{word} =~ /^\d+$/);
        "I say a word: ".params->{word};

    get '/say/:number' => sub {
        "I say a number: ".params->{number};


The action's return value is always considered to be the content to render. So take care to your return value.

In order to change the default behaviour of the rendering of an action, you can use the following keywords.


By default, an action will produce an 'HTTP 200 OK' status code, meaning everything is OK. It's possible to change that with the keyword status :

    get '/download/:file' => {
        if (! -f params->{file}) {
            status 'not_found';
            return "File does not exist, unable to download";
        # serving the file...

In that example, Dancer will notice that the status has changed, and will render the response accordingly.

The status keyword receives the name of the status to render, it can be either an HTTP code or its alias, as defined in Dancer::HTTP.


You can also change the content type rendered in the same maner, with the keyword content_type

    get '/cat/:txtfile' => {
        content_type 'text/plain';

        # here we can dump the contents of params->{txtfile}



When an error is renderered (the action responded with a status code different than 200), Dancer first looks in the public directory for an HTML file matching the error code (eg: 500.html or 404.html).

If such a file exists, it's used to render the error, otherwise, a default error page will be rendered on the fly.


When an error occurs during the route execution, Dancer will render an error page with the HTTP status code 500.

It's possible either to display the content of the error message or to hide it with a generic error page.

This is a choice left to the end-user and can be set with the show_errors setting.

Note that you can also choose to consider all warnings in your route handlers as errors when the setting warnings is set to 1.


Before filters

Before filters are evaluated before each request within the context of the request and can modify the request and response. It's possible to define variable that will be accessible in the action blocks with the keyword 'var'.

    before sub {
        var note => 'Hi there';
    get '/foo/*' => sub {
        my ($match) = splat; # 'oversee';
        vars->{note}; # 'Hi there'

The request keyword returns the current CGI object representing the incoming request. See the documentation of the CGI module for details.


Configuring a Dancer application can be done in many ways. The easiest one (and maybe the the dirtiest) is to put all your settings statements at the top of your script, before calling the dance() method.

Other ways are possible, you can write all your setting calls in the file `appdir/config.yml'. For this, you must have installed the YAML module, and of course, write the conffile in YAML.

That's better than the first option, but it's still not perfect as you can't switch easily from an environment to another without rewriting the config.yml file.

The better way is to have one config.yml file with default global settings, like the following:

    # appdir/config.yml
    logger: 'file'
    layout: 'main'

And then write as many environment file as you like in appdir/environements. That way, the good environment config file will be loaded according to the running environment (if none specified, it will be 'development').

Note that you can change the running environment using the --environment commandline switch.

Typically, you'll want to set the following values in a development config file:

    # appdir/environments/development.yml
    log: 'debug'
    access_log: 1

And in a production one:

    # appdir/environments/production.yml
    log: 'warning'
    access_log: 0


It's possible to log messages sent by the application. In the current version, only one method is possible for logging messages but it may come in future releases new methods.

In order to enable the logging system for your application, you first have to start the logger engine in your config.yml

    log: 'file'

Then you can choose which kind of messages you want to actually log:

    log: 'debug'     # will log debug, warning and errors
    log: 'warning'   # will log warning and errors
    log: 'error'     # will log only errors

A directory appdir/logs will be created and will host one logfile per environment. The log message contains the time it was written, the PID of the current process, the message and the caller information (file and line).



It's possible to render the action's content with a template, this is called a view. The `appdir/views' directory is the place where views are located.

You can change this location by changing the setting 'views', for instance if your templates are located in the 'templates' directory, do the following:

    set views => path(dirname(__FILE__), 'templates');

A view should have a '.tt' extension and is rendered with the Template module. You have to import the `Template' module in your script if you want to render views within your actions.

In order to render a view, just call the 'template' keyword at the end of the action by giving the view name and the HASHREF of tokens to interpolate in the view (note that all the route params are accessible in the view):

    use Dancer;
    use Template;

    get '/hello/:name' => sub {
        template 'hello' => {var => 42};

And the appdir/views/hello.tt view can contain the following code:

        <h1>Hello <% params.name %></h1>


A layout is a special view, located in the 'layouts' directory (inside the views directory) which must have a token named `content'. That token marks the place where to render the action view. This lets you define a global layout for your actions.

Here is an example of a layout: views/layouts/main.tt :

        <div id="header">

        <div id="content">
        <% content %>


This layout can be used like the following:

    use Dancer;
    use Template; 

    layout 'main';

    get '/' => sub {
        template 'index';



Static files are served from the ./public directory. You can specify a different location by setting the 'public' option:

    set public => path(dirname(__FILE__), 'static');

Note that the public directory name is not included in the URL. A file ./public/css/style.css is made available as example.com/css/style.css.


By default, Dancer will automatically detect the mime-types to use for the static files accessed.

It's possible to choose specific mime-type per file extensions. For instance, we can imagine you want to sever *.foo as a text/foo content, instead of text/plain (which would be the content type detected by Dancer if *.foo are text files).

        mime_type foo => 'text/foo';

This configures the 'text/foo' content type for any file matching '*.foo'.


It's possible for a route handler to pass the batton to a static file, like the following.

    get '/download/*' => sub {
        my $params = shift;
        my ($file) = @{ $params->{splat} };

        send_file $file;

Or even if you want your index page to be a plain old index.html file, just do:

    get '/' => sub {
        send_file '/index.html'


It's possible to change quite every parameter of the application via the settings mechanism.

A setting is key/value pair assigned by the keyword set:

    set setting_name => 'setting_value';

See Dancer::Config for complete details about supported settings.


This is a possible webapp created with Dancer :

    # make this script a webapp
    use Dancer;

    # declare routes/actions
    get '/' => sub { 
        "Hello World";

    get '/hello/:name' => sub {
        "Hello ".params->{name}"

    # run the webserver


This module has been written by Alexis Sukrieh <sukria@cpan.org>


The source code for this module is hosted on GitHub http://github.com/sukria/Dancer


Dancer depends on the following modules:

The following modules are mandatory (Dancer cannot run without them)


The following modules are optional

Template needed for the views rendering system
Logger::Syslog needed for logging information to syslog


This module is free software and is published under the same terms as Perl itself.


The concept behind this module comes from the Sinatra ruby project, see http://www.sinatrarb.com for details.