ikiwiki [[plugins]] are written in perl. Each plugin is a perl module, in the `IkiWiki::Plugin` namespace. The name of the plugin is typically in lowercase, such as `IkiWiki::Plugin::inline`. Ikiwiki includes a `IkiWiki::Plugin::skeleton` that can be fleshed out to make a useful plugin. `IkiWiki::Plugin::pagecount` is another simple example. ## Note One thing to keep in mind when writing a plugin is that ikiwiki is a wiki *compiler*. So plugins influence pages when they are built, not when they are loaded. A plugin that inserts the current time into a page, for example, will insert the build time. Also, as a compiler, ikiwiki avoids rebuilding pages unless they have changed, so a plugin that prints some random or changing thing on a page will generate a static page that won't change until ikiwiki rebuilds the page for some other reason, like the page being edited. ## Registering plugins Plugins should, when imported, call IkiWiki::register_plugin to hook into ikiwiki. The function takes four parameters: 1. A method type. Use "preprocess" to register a [[PreProcessorDirective]] 2. A command name. This is the bit that will appear inside brackets in a page. 3. A reference to a subroutine that is run when the plugin is used. ## Writing a [[PreProcessorDirective]] For preprocessor directives, the subroutine is passed named parameters. A "page" parameter gives the name of the page that embedded the preprocessor directive. All parameters included in the directive are included as named parameters as well. Whatever the subroutine returns goes onto the page in place of the directive. ## Error handing in plugins While a plugin can call ikiwiki's error routine for a fatal error, for errors that aren't intended to halt the entire wiki build, including bad parameters passed to a [[PreProcessorDirective]], etc, it's better to just return the error message as the output of the plugin. ## Html issues Note that if [[HTMLSanitization]] is enabled, html in [[PreProcessorDirective]] output is sanitised, which may limit what your plugin can do. Also, the rest of the page content is not in html format at preprocessor time. ## Wiki configuration A plugin can access the wiki's configuration via the `%IkiWiki::config` hash. The best way to understand the contents of the hash is to look at [[ikiwiki.setup]], which sets the hash content to configure the wiki. ## Wiki data If your plugin needs to access data about other pages in the wiki. It can use the following hashes, using a page name as the key: * `%IkiWiki::links` lists the names of each page that is linked to from that page in an array reference. * `%IkiWiki::pagemtime` contains the last modification time of each page * `%IkiWiki::pagectime` contains the creation time of each page` * `%IkiWiki::renderedfiles` contains the name of the file rendered by a page * `%IkiWiki::pagesources` contains the name of the source file for a page. * `%IkiWiki::depends` contains a [[GlobList]] that is used to specify other pages that a page depends on. If one of its dependencies is updated, the page will also get rebuilt. Many plugins will need to add dependencies to this hash; the best way to do it is by using the IkiWiki::add_depends function, which takes as its parameters the page name and a [[GlobList]] of dependencies to add.