Unix supports a wider variety of application languages than does any other single operating system; indeed, it may well have hosted more different languages than every other operating system in the history of computing combined.^[122]

There are at least two excellent reasons for this huge diversity. One is the wide use of Unix as a research and teaching platform. The other (far more relevant for working programmers) is the fact that matching your application design with the proper implementation language(s) can make an immense difference in your productivity. Therefore the Unix tradition encourages the design of domain-specific languages (as we mentioned in Chapter 7 and Chapter 9) and what are now generally called scripting languages—those designed specifically to glue together other applications and tools.

In truth, the term ‘scripting language’ is a somewhat awkward one. Many of the the major languages usually so described (Perl, Tcl, Python, etc.) have outgrown the group's scripting origins and are now standalone general-purpose programming languages of considerable power. The term tends to obscure strong similarities in style with other languages that are not usually lumped in with this group, notably Lisp and Java. The only argument for continuing to use it is that nobody has yet invented a better term.

Part of the reason all these can be lumped together under the rubric of ‘scripting language’ is that they all have pretty much the same ontogeny. Having a runtime to do interpretation also makes it relatively easy to automate dynamic storage management. Automating dynamic storage management almost requires using references (opaque memory addresses that you can't do arithmetic on) rather than passing value copies or explicit pointers around. Using references makes runtime polymorphism and OO an easy next step. Voila: the modern scripting language!

To apply the Unix philosophy effectively, you'll need to have more than just C in your toolkit. You'll need to learn how to use some of Unix's other languages (especially the scripting languages), and how to be comfortable mixing multiple languages in specialist roles within large program systems.

In this chapter we'll survey C and its most important alternatives, discussing their strengths and weaknesses and the sorts of tasks to which they are best matched. The languages covered will be C, C++, shell, Perl, Tcl, Python, Java, and Emacs Lisp. Each survey section will include case studies on applications written using these languages, and references to other examples and tutorial material. High-quality implementations of all these languages are available in open source on the Internet.

Warning: Choice of application language is one of the archetypal religious issues in the Internet/Unix world. People get very attached to these tools and will sometimes defend them past all reason. If this chapter achieves its aim, zealots of all stripes may be offended by this chapter, but everyone else will learn from it.