A Web-Based Clipping Service
Now that we have a program to retrieve documents that fit our criteria, how can we use it? We could run it from the command line, but the point of this program is to do your work for you, downloading documents while you sleep or watch television.
The easiest way is to use cron, the Linux facility that allows us to run programs at regular intervals. Each user has his or her own crontab, a table that indicates when a program should be run. Each command is preceded by five columns that indicate the time and date on which a program should be run: the minute, hour, day of month, month and day of the week. These columns are normally filled with numbers, but an asterisk can be used to indicate a wild card.
The following entry in a crontab indicates the program /bin/foo should be run every Sunday at 4:05 A.M.:
5 4 * * 0 /bin/foo
Be sure to use a complete path name when using cron—here we indicated /bin/foo, rather than just “foo”.
The crontab is edited with the crontab program, using its -e option. This will open the editor defined in the EDITOR environment variable, which is vi by default. (Emacs users should consider setting this to emacsclient, which loads the file in an already running Emacs process.)
To download all of the files matching our phrases from Wired News every day at midnight, we could use the following:
0 0 * * 0 /usr/bin/download-matching.pl\ www.wired.com/news/http://www.wired.com/news/
This will start the process of downloading files from http://www.wirec.com/news/ at midnight, placing the results in $output_directory. We can specify multiple URLs as well, allowing us to retrieve news from more than one of our favorite news sources. When we wake up in the morning, new documents that interest us will be waiting for us to read, sitting in $output_directory.
Many organizations hire clipping services to find news that is of interest to them. With a bit of cleverness and heavy reliance on LWP, we can create our own personalized clipping service, downloading documents that reflect our personal interests. No longer must you look through a list of headlines in order to find relevant documents—let Perl and the Web do your work for you.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
Free to Linux Journal readers.Register Now!
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide