A bit about cron

Written by Tron Hvaring of Norway back in 1994, cron version 1.9 is a DOS-based equivalent of the indispensable Unix cron utility. cron reads a text file of commands and scheduling information, then selects the next task to perform.  It maintains a display on the console so you can see when the next task will start. At the appointed time, cron suspends itself, then launches the task.  When the task completes, cron resumes, displaying the next task to be done.

Setting up cron is straightforward, and Tron provides an excellent reference manual with the distribution.  I won't go into a lot of detail here, but I'll mention a few minor points, already well covered in Tron's docs.  Use the -v option when you invoke cron, so you can see the countdown timer and task list on the console.

If you have any crashing problems with cron, it is likely because you aren't using the '!' operator correctly in your task definition line.  The '!' operator forces cron to run a new copy of command.com when it starts a task, and some DOS operations require a new copy, some don't.  As Tron points out, all of the internal commands, such as cd or type, require the '!' operator.  If you need to run a batch file as a task, and have to change directories to do it, call out the batch file by its full path name in the cron task, then include the cd command at the top of the batch file.

Note that cron takes full control of your computer when it runs; cron is not a multitasker.  This isn't a problem for an automatic data collector, as it isn't going to be doing anything else, anyway.  If you ever need to halt cron, just hit the Escape key.

You can download a copy of cron here, or you can find a copy of cron in the ms-dos/schedule areas of any of the SimTel mirror sites.  Look for the file cron19.zip.

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