The Tcl Development Process

Creating new Tcl scripts is very easy. There are two ways to create Tcl scripts:

• You can create a file in the pages directory for any virtual server (see the PageRoot parameter in the configuration file) with a .tcl extension that contains Tcl commands.

  To run your script, just get the "page" consisting of your script in any browser. For example, if you created a file called mytest.tcl in the pages directory for a virtual server, just type http://www.yourorg.com/mytest.tcl in the URL field of your browser. The results will be displayed in your page.

  This method is useful if you just want to execute Tcl commands without binding them to specific URL requests as procedures.

• You can use AOLserver's simple HTML forms interface to create, update, and immediately load a Tcl script into the running server. This method allows you to bind a Tcl procedure as an operation to handle one or more URL requests. It's not quite as simple as putting a .tcl file in your pages directory, but it is more powerful. The statements that define the URL-handling procedures and bind the procedures to URLs are normally stored in script files in the appropriate subdirectory of the AOLserver home directory.

  At startup, AOLserver determines the Tcl directory for each virtual server by searching the directories listed in the order below:

  • the directory specified by the Library configuration parameter

  • the /servers/server-name/modules/tcl directory under the AOLserver home directory

  • the directory specified by the SharedLibrary configuration

  • the /modules/tcl directory under the AOLserver home directory

By default, all script files in this directory that end with the .tcl extension are automatically sourced by the AOLserver at server startup time. This process is termed Tcl Initialization. Because the statements included in the scripts files can normally be re-sourced at any time, it is possible to modify or add new script files to the Tcl directory while the server is running and re-initialize Tcl. The AOLserver provides an operation for this purpose, itself written in Tcl, which is accessed by opening the /NS/TclInit URL. Each of the AOLserver modules has it's own subdirectory in the Tcl directory, and you can specify that AOLserver initialize a specific subdirectory using /NS/TclInit/subdirectory. /NS/TclInit is not recursive in that it does not automatically initialize Tcl scripts in subdirectories below the one specified.

The AOLserver also provides operations for opening an existing or new Tcl script in an HTML form where you can update it and submit it for evaluation by the server. You can use any browser to create, edit, and update your Tcl extensions. The easiest way to get started is to use a browser to bring up the AOLserver Administration page. From AOLpress, go to Tools Administer Server, and select the name of your server (e.g., http://www.yourorg.com/). From any other browser, go to the relative URL /NS/Admin on your server (e.g., http:// www.yourorg.com/NS/Admin). At the bottom of the page, follow the link to Tcl Scripting, and then follow the link to View/Edit Shared Script Files. The AOLserver lists all Tcl files in the Tcl subdirectory specified in the configuration file with links to view and/or update those script files.

Many of the basic AOLserver services are implemented as Tcl scripts. In fact, most of the database operations such as handling database inserts, queries, and updates, are written as Tcl scripts. You can easily modify the basic database operations by simply editing the Tcl scripts that implement the functionality.

The following section is a tutorial on developing new operations in the AOLserver Tcl interface. The examples are a quick and fun way to get to an overview of the Tcl scripting process.

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