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Mason - High-performance, dynamic web site authoring system


    PerlModule HTML::Mason::ApacheHandler

    <Location />
        SetHandler perl-script
        PerlHandler HTML::Mason::ApacheHandler


Mason is a tool for building, serving and managing large web sites. Its features make it an ideal backend for high load sites serving dynamic content, such as online newspapers or database driven e-commerce sites.

Actually, Mason can be used to generate any sort of text, whether for a web site or not. But it was originally built for web sites and since that's why most people are interested in it, that is the focus of this documentation.

Mason's various pieces revolve around the notion of "components''. A component is a mix of HTML, Perl, and special Mason commands, one component per file. So-called "top-level" components represent entire web-pages, while smaller components typically return HTML snippets for embedding in top-level components. This object-like architecture greatly simplifies site maintenance: change a shared component, and you instantly changed all dependant pages that refer to it across a site (or across many virtual sites).

Mason's component syntax lets designers separate a web page into programmatic and design elements. This means the esoteric Perl bits can be hidden near the bottom of a component, preloading simple variables for use above in the HTML. In our own experience, this frees content managers (i.e., non-programmers) to work on the layout without getting mired in programming details. Techies, however, still enjoy the full power of Perl.

Mason works by intercepting innocent-looking requests (say, and mapping them to requests for Mason components. Mason then compiles the component, runs it, and feeds the output back to the client.

Consider this simple Mason component:

    % my $noun = 'World';
    Hello <% $noun %>!
    How are ya?

The output of this component is:

    Hello World!
    How are ya?

In this component you see a mix of standard HTML and Mason elements. The bare '%' prefixing the first line tells Mason that this is a line of Perl code. One line below, the embedded <% ... %> tag gets replaced with the return value of its contents, evaluated as a Perl expression.

Beyond this trivial example, components can also embed serious chunks of Perl code (say, to pull records from a database). They can also call other components, cache results for later reuse, and perform all the tricks you expect from a regular Perl program.


Mason has been tested under Linux, FreeBSD, Solaris, HPUX, and Win32. As an all-Perl solution, it should work on any machine that has working versions of Perl 5.00503+, mod_perl, and the required CPAN modules.

Mason has a standard MakeMaker-driven installation. See the README file for details.


This section assumes that you are able to install and configure a mod_perl server. Relevant documentation is available at (Apache) and (mod_perl). The mod_perl mailing list, archive, and guide are also great resources.

The simplest configuration of Mason requires a few lines in your httpd.conf:

    PerlModule HTML::Mason::ApacheHandler

    <Location />
        SetHandler perl-script
        PerlHandler HTML::Mason::ApacheHandler

The PerlModule directive simply ensures that the Mason code is loaded in the parent process before forking, which can save some memory when running mod_perl.

The <Location> section routes all requests to the Mason handler, which is a simple way to try out Mason. A more refined setup is discussed in the Controlling Access via Filename Extension section of the administrator's manual.

Once you have added the configuration directives, restart the server. First, go to a standard URL on your site to make sure you haven't broken anything. If all goes well you should see the same page as before. If not, recheck your Apache config files and also tail your server's error log.

If you are getting "404 Not Found" errors even when the files clearly exist, Mason may be having trouble with your document root. One situation that will unfortunately confuse Mason is if your document root goes through a symbolic link. Try expressing your document root in terms of the true filesystem path.

Next, try adding the tag <% 2+2 %> at the top of some HTML file. If you reload this page and see a "4", Mason is working!


Once Mason is on its feet, the next step is to write a component or two. The Mason Developer's Manual is a complete tutorial for writing, using, and debugging components. A reference companion to the Developer's Manual is the Request API documentation, HTML::Mason::Request.

Whoever is responsible for setting up and tuning Mason should read the Administrator's Manual, though developers will also benefit from reading it as well. This document covers more advanced configuration scenarios and performance optimization. The reference companion to the Administrator's manual is the Parameters Reference, which describes all the parameters you can use to configure Mason.

Most of this documentation assumes that you're running Mason on top of mod_perl, since that is the most common configuration. If you would like to run Mason via a CGI script, refer to the HTML::Mason::CGIHandler documentation. If you are using Mason from a standalone program, refer to the Using Mason from a Standalone Script section of the administrator's manual.

There is also a book about Mason, Embedding Perl in HTML with Mason, by Dave Rolsky and Ken Williams, published by O'Reilly and Associates. The book's website is at This book goes into detail on a number of topics, and includes a chapter of recipes as well as a sample Mason-based website.


Jonathan Swartz <>, Dave Rolsky <>, Ken Williams <>


HTML::Mason::Devel, HTML::Mason::Admin