When to Use Tcl Libraries

The alternative to embedding Tcl scripts in HTML pages using ADPs (see Chapter 2), is to store Tcl scripts in Tcl libraries. The situations listed below are well suited to the Tcl libraries approach.

• Inheritance: If you want one Tcl script to handle an URL and all of its sub-URLs, it's better to store the script in a Tcl library and register it using ns_register_proc to handle an URL hierarchy. For example, you may want to manage a server domain name change by redirecting every response to the corresponding domain name on another server.

• Special Extensions: If you want one Tcl script to handle all files with a specific extension, like /*.csv, you would register the script with ns_register_proc to handle those files.

• Scheduled Procedures: If you want a Tcl script to be run at specific intervals, you can use the ns_schedule_* functions to run a script from the Tcl library at scheduled intervals. These procedures do not normally involve returning HTML pages and so are not well suited to ADPs.

• Filters: If you want a Tcl script to be called at pre-authorization, post-authorization, or trace time for a group of URLs, you would register a filter using the ns_register_filter function.

• Re-using Tcl Scripts: If there are Tcl scripts that you want to use in multiple situations, you can store them in a Tcl library and invoke them from within any ADP or Tcl script.