Classic Shell Scripting

Chapter 2. Getting Started

When you need to get some work done with a computer, it's best to use a tool that's appropriate to the job at hand. You don't use a text editor to balance your checkbook or a calculator to write a proposal. So too, different programming languages meet different needs when it comes time to get some computer-related task done.

Shell scripts are used most often for system administration tasks, or for combining existing programs to accomplish some small, specific job. Once you've figured out how to get the job done, you can bundle up the commands into a separate program, or script, which you can then run directly. What's more, if it's useful, other people can make use of the program, treating it as a black box, a program that gets a job done, without their having to know how it does so.

In this chapter we'll make a brief comparison between different kinds of programming languages, and then get started writing some simple shell scripts.

Scripting Languages Versus Compiled Languages

Most medium and large-scale programs are written in a compiled language, such as Fortran, Ada, Pascal, C, C++, or Java. The programs are translated from their original source code into object code which is then executed directly by the computer's hardware.^[1]

The benefit of compiled languages is that they're efficient. Their disadvantage is that they usually work at a low level, dealing with bytes, integers, floating-point numbers, and other machine-level kinds of objects. For example, ...