Tcl includes a library of Tcl procedures for commonly-needed functions. The procedures defined in the Tcl library are generic ones suitable for use by many different applications. The location of the Tcl library is returned by the info library command. In addition to the Tcl library, each application will normally have its own library of support procedures as well; the location of this library is normally given by the value of the $app_library global variable, where app is the name of the application. For example, the location of the Tk library is kept in the variable $tk_library.
To access the procedures in the Tcl library, an application should
source the file init.tcl in the library, for example with
the Tcl command
source [info library ]/init.tcl
This will define the unknown procedure and arrange for the other procedures to be loaded on-demand using the auto-load mechanism defined below.