Dave Taylor

I'm a rabid Linux fan. I write books about it, I have servers running it, and I even have various flavors of Linux as dual-boot defaults on my PCs. But keeping up with Linux news can be a bit of effort, particularly if I want to have that up-to-date news on a Web page, rather than in an RSS Aggregator. Fortunately, it's a matter of ten minutes of shell script programming to remedy this. In this article, I'll show you step-by-step exactly how to create a cron job that'll automatically create an HTML file that contains the latest headlines from LinuxWorld.com. Just don't tell their Webmaster! :-) Getting to the Right Page Like many sites, LinuxWorld.com has "XML" buttons on its various category pages, so it takes only a few seconds to identify that http://www.linuxworld.com/topic_content/c_news.rss is the URL of the RSS feed for LinuxWorld.com's news. Now, to tap into ... (more)

Loops Within Loops: "hilow.sh"

If the print gods are with us, this time, after seven previous columns, we'll finally have a shell script that you can type in and experiment with. Imagine! The last column addressed the challenges of generating a reasonably random number to enable us to write a rudimentary hi-low guessing game. After experimentation, we settled on using the date command with some fancy footwork to generate a number between 1..x as shown here: toguess="$(expr `date +%S` % 20 + 1)" In this case, the result is a quasi-random number between 1 and 20. Good enough for our game, which involves the com... (more)

Dual Booting Linux on a Mac

What happens when you turn a perfectly good Apple PowerBook into a tri-boot system with Mac OS X, Yellow Dog Linux, and Ubuntu Linux? Read on to find out. Mac OS X is built of two components: Darwin, the BSD-based Unix underpinnings, and Aqua, the beautiful graphical user interface we Mac heads have all grown to love. However, there are other operating systems and other work environments that can be installed on an Apple system, based on popular open source Linux applications. If you're looking for Intel-based versions of Linux, there are dozens and dozens, but the PowerPC chip... (more)

String and Numeric Test Statements

Last month I talked about the file-related options to the test command and how that helps you create smart and sophisticated shell scripts. This time I want to look at the additional conditions available for looping and flow control. String TestsOne common test in shell scripts is to ascertain whether something the user has typed in or something pulled out of a data stream or file matches a specific pattern or string. The first of these tests is -z $string, which returns true if the string is zero length, false otherwise. Consider this snippet: empty="" if [ -z $empty ] ; then e... (more)

Making C Shell Jump Through Hoops

By this point in our discussion you should be comfortable with the idea of the three file descriptors associated with the Linux command line: stdin, stdout, and stderr (pronounced "standard in," "standard out," and "standard error"). If you're using a descendant of the Bourne Shell (such as Bash), you also learned last month how to use the x>&y notation to redirect the different descriptors from the command line, and therefore from within a script too. This time I'll turn my attention to the C shell with its different command-line syntax. My focus here is ultimately on shell scr... (more)