Because so much open source is available in the Unix world, skill at finding code to reuse can have an enormous payoff — much greater than is the case for other operating systems. Such code comes in many forms: individual code snippets and examples, code libraries, utilities to be reused in scripts. Under Unix most code reuse is not a matter of actual cut-and-paste into your program — in fact, if you find yourself doing that, there is almost certainly a more graceful mode of reuse that you are missing. Accordingly, one of the most useful skills to cultivate under Unix is a good grasp of all the different ways to glue together code, so you can use the Rule of Composition.

To find re-usable code, start by looking under your nose. Unixes have always featured a rich toolkit of re-usable utilities and libraries; modern ones, such as any current Linux system, include thousands of programs, scripts, and libraries that may be re-usable. A simple man -k search with a few keywords often yields useful results.

To begin to grasp something of the amazing wealth of resources out there, surf to SourceForge, ibiblio, and Freshmeat.net. Other sites as important as these three may exist by the time you read this book, but all three of these have shown continuing value and popularity over a period of years, and seem likely to endure.

SourceForge is a demonstration site for software specifically designed to support collaborative development, complete with associated project-management services. It is not merely an archive but a free development-hosting service, and in mid-2003 is undoubtedly the largest single hub of open-source activity in the world.

The Linux archives at ibiblio were the largest in the world before SourceForge. The ibiblio archives are passive, simply a place to publish packages. They do, however, have a better interface to the World Wide Web than most passive sites (the program that creates its Web look and feel was one of our case studies in the discussion of Perl in Chapter 14). It's also the home site of the Linux Documentation Project, which maintains many documents that are excellent resources for Unix users and developers.

Freshmeat is a system dedicated to providing release announcements of new software, and new releases of old software. It lets users and third parties attach reviews to releases.

These three general-purpose sites contain code in many languages, but most of their content is C or C++. There are also sites specialized around some of the interpreted languages as discussed in Chapter 14.

The CPAN archive is the central repository for useful free code in Perl. It is easily reached from the Perl home page.

The Python Software Activity makes an archive of Python software and documentation available at the Python Home Page.

Many Java applets and pointers to other sites featuring free Java software are made available at the Java Applets page.

One of the most valuable ways you can invest your time as a Unix developer is to spend time wandering around these sites learning what is available for you to use. The coding time you save may be your own!

Browsing the package metadata is a good idea, but don't stop there. Sample the code, too. You'll get a better grasp on what the code is doing, and be able to use it more effectively.

More generally, reading code is an investment in the future. You'll learn from it — new techniques, new ways to partition problems, different styles and approaches. Both using the code and learning from it are valuable rewards. Even if you don't use the techniques in the code you study, the improved definition of the problem you get from looking at other peoples' solutions may well help you invent a better one of your own.

Read before you write; develop the habit of reading code. There are seldom any completely new problems, so it is almost always possible to discover code that is close enough to what you need to be a good starting point. Even when your problem is genuinely novel, it is likely to be genetically related to a problem someone else has solved before, so the solution you need to develop is likely to be related to some pre-existing one as well.