This post originated from an RSS feed registered with Web Buzz by Douglas Clifton. Original Post: Advanced crontab Tutorial Feed Title: blogZero Feed URL: http://loadaveragezero.com/app/s9y/index.php?/feeds/index.rss1 Feed Description: Web Development News, Culture and Opinion Latest Web Buzz Posts Latest Web Buzz Posts by Douglas Clifton Latest Posts From blogZero

Most crontab entries are very simple. For instance, "run this script once every day exactly at midnight." To do this you would add the following line to your crontab file:

0 0 * * * /path/to/script

Depending on your version of cron, you could also use the shorthand string @midnight or @daily. But what if you need to run a script between the hours of 8am and 6pm every two hours, but only on Mondays through Saturdays? That's exactly the problem I had to solve earlier today. Although I use cron quite a bit, I needed a quick syntax refresher course covering some of the more advanced features.

So naturally (like we all do) I reached for my browser and fired up Google. After 20 wasted minutes trying various keyword search combinations, wading several result pages deep and following links, it hit me. Do'h! All the information I needed was right on my FreeBSD server. Man pages contain a wealth of information about your system and have been around for many years. Decades actually. Many people forget that Unix was originally designed as a text processing and technical manual printing system. The entire system is documented using these manual pages and they are designed for viewing, searching and printing. I once kept large chunks of the standard C library in a 3-ring binder.

Since crontab is a file format, I went back to my shell and entered:

$ man 5 crontab

And within a matter of minutes I had the solution. The point of all of this is sometimes we are over reliant on the Web and search. Often the information we are seeking has been there all along. Call me old school, I still like books too.

By the way, the crontab entry looks like this:

0 8-18/2 * * 1-6 /path/to/script

If you really have to use a browser, try this "advanced crontab tutorial."

How ironic, I posted this exactly at midnight.