Purpose: discuss some of the connections between Tcl and the cron facility

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Cron is an application available on many platforms designed to allow one to schedule invocations of applications at set calendar date and times on a computer.

When an application is invoked, it appears to run as a particular user, '''BUT''' with a minimal environment variable setup and typically in a preset command shell.

The limited environmental shell setup is the first problem users typically encounter - they expect that they will find various variables that are set during their machine's startup environment during login, or their own personalized login environment - but those are not present.

Thus one must decide to take one of two courses of action:

   * write the application in such a way that it needs no special variables
   * set the special variables up that may be needed
   * create some sort of wrapper application that presets the operational environment

What kinds of variables might be needed?  Well, for instance, special $PATH values, database pointer variables, printer names, etc. all may need to be set up.

What else can go wrong?

Some applications expect certain terminal settings - some place to write output, some place to prompt for input, perhaps access to some other special device (like an X Window display!).  It is often the user will find that they have dependencies (via subroutines or other invoked applications) that they weren't even aware existed.