Core API

2.1.6. Import and install of extensions

There are only two (maybe three) simple steps involved in using extensions with TYPO3:

1. You must import it.
   This simply means to copy the extensions files into the correct directory in either typo3/ext/ (global) or typo3conf/ext/ (local). More commonly you import an extension directly from the online TYPO3 Extension Repository. When an extension is found located in one of the extension locations, it is available to the system.
   The EM should take care of this process, including updates to newer versions if needed.
   Notice that backend modules will have their "conf.php" file modified in the install process depending on whether they are installed locally or globally!

2. You must install it.
   An extension is loaded only if its extension key is listed in comma list of the variable $TYPO3_CONF_VARS["EXT"]["extList"]. The list of enabled extensions must be set and modified from inside typo3conf/localconf.php. Extensions are loaded in the order they appear in this list. Any extensions listed in $TYPO3_CONF_VARS["EXT"]["requiredExt"] will be forcibly loaded before any extensions in $TYPO3_CONF_VARS["EXT"]["extList"].
   An enabled extension is always global to the TYPO3 Installation - you cannot disable an extension from being loaded in a particular branch of the page tree.
   The EM takes care enabling extensions. It's highly recommended that the EM is doing this, because the EM will make sure the priorities, dependencies and conflicts are managed according to the extension characteristics, including clearing of the cache-files if any.

3. You might need to configure it.
   Certain extensions may allow you to configure some settings. Again the EM is able to handle the configuration of the extensions based on a certain API for this. Any settings - if present - configured for an extension is available as an array in the variable $TYPO3_CONF_VARS["EXT"]["extConf"][extension key].

Loaded extensions are registered in a global variable, $TYPO3_LOADED_EXT, available in both frontend and backend of TYPO3. The loading and registration process happens in t3lib/config_default.php.

This is how the data structure for an extension in this array looks:

  $TYPO3_LOADED_EXT[extension key] = Array (

      "type" =>        S, G, L for system, global or local type of availability.

      "siteRelPath" => Path of extension dir relative to the PATH_site constant

                  eg. "typo3/ext/my_ext/" or "typo3conf/ext/my_ext/"

      "typo3RelPath" => Path of extension dir relative to the "typo3/" admin folder

                  eg. "ext/my_ext/" or "../typo3conf/ext/my_ext/"

      "ext_localconf" => Contains absolute path to 'ext_localconf.php' file if present

      "ext_tables" => [same]

      "ext_tables_sql" => [same]

      "ext_tables_static+adt.sql" => [same]

      "ext_typoscript_constants.txt" => [same]

      "ext_typoscript_setup.txt" => [same]

      "ext_typoscript_editorcfg.txt" => [same]

  )

 

The order of the registered extensions in this array corresponds to the order they were listed in TYPO3_CONF_VARS["EXT"]["requiredExt"].TYPO3_CONF_VARS["EXT"]["extList"] with duplicates removed of course.

The inclusion of ext_tables.php or ext_localconf.php files are done by traversing (a copy of) the $TYPO3_LOADED_EXT array.