Beginning Linux Programming

Neil Matthew, Richard Stones

• Publisher: Wrox
• Year: 2011
• ISBN:
  9781118058619
• Edition: 4
• Topic: Computer Science
• Subtopic: Operating Systems
• Index: Computer Science

Beginning Linux Programming, Fourth Edition continues its unique approach to teaching UNIX programming in a simple and structured way on the Linux platform. Through the use of detailed and realistic examples, students learn by doing, and are able to move from being a Linux beginner to creating custom applications in Linux. The book introduces fundamental concepts beginning with the basics of writing Unix programs in C, and including material on basic system calls, file I/O, interprocess communication (for getting programs to work together), and shell programming. Parallel to this, the book introduces the toolkits and libraries for working with user interfaces, from simpler terminal mode applications to X and GTK+ for graphical user interfaces. Advanced topics are covered in detail such as processes, pipes, semaphores, socket programming, using MySQL, writing applications for the GNOME or the KDE desktop, writing device drivers, POSIX Threads, and kernel programming for the latest Linux Kernel.

Chapter 1

Getting Started

In this chapter, you discover what Linux is and how it relates to its inspiration, UNIX. You take a guided tour of the facilities provided by a Linux development system, and write and run your first program. Along the way, you’ll be looking at

• UNIX, Linux, and GNU
• Programs and programming languages for Linux
• How to locate development resources
• Static and shared libraries
• The UNIX philosophy

An Introduction to UNIX, Linux, and GNU

In recent years Linux has become a phenomenon. Hardly a day goes by without Linux cropping up in the media in some way. We’ve lost count of the number of applications that have been made available on Linux and the number of organizations that have adopted it, including some government departments and city administrations. Major hardware vendors like IBM and Dell now support Linux, and major software vendors like Oracle support their software running on Linux. Linux truly has become a viable operating system, especially in the server market.

Linux owes its success to systems and applications that preceded it: UNIX and GNU software. This section looks at how Linux came to be and what its roots are.

What Is UNIX?

The UNIX operating system was originally developed at Bell Laboratories, once part of the telecommunications giant AT&T. Designed in the 1970s for Digital Equipment PDP computers, UNIX has become a very popular multiuser, multitasking operating system for a wide variety of hardware platforms, from PC workstations to multiprocessor servers and supercomputers.

A Brief History of UNIX

Strictly, UNIX is a trademark administered by The Open Group, and it refers to a computer operating system that conforms to a particular specification. This specification, known as The Single UNIX Specification, defines the names of, interfaces to, and behaviors of all mandatory UNIX operating system functions. The specification is largely a superset of an earlier series of specifications, the P1003, or POSIX (Portable Operating System Interface) specifications, developed by the IEEE (Institute of Electrical and Electronic Engineers).

Many UNIX-like systems are available commercially, such as IBM’s AIX, HP’s HP-UX, and Sun’s Solaris. Some have been made available for free, such as FreeBSD and Linux. Only a few systems currently conform to The Open Group specification, which allows them to be marketed with the name UNIX.

In the past, compatibility among different UNIX systems has been a real problem, although POSIX was a great help in this respect. These days, by following a few simple rules it is possible to create applications that will run on all UNIX and UNIX-like systems. You can find more details on Linux and UNIX standards in Chapter 18.

UNIX Philosophy

In the following chapters we hope to convey a flavor of Linux (and therefore UNIX) programming. Although programming in C is in many ways the same whatever the platform, UNIX and Linux developers have a special view of program and system development.

The UNIX operating system, and hence Linux, encourages a certain programming style. Following are a few characteristics shared by typical UNIX programs and systems:

• Simplicity: Many of the most useful UNIX utilities are very simple and, as a result, small and easy to understand. KISS, “Keep It Small and Simple,” is a good technique to learn. Larger, more complex systems are guaranteed to contain larger, more complex bugs, and debugging is a chore that we’d all like to avoid!
• Focus: It’s often better to make a program perform one task well than to throw in every feature along with the kitchen sink. A program with “feature bloat” can be difficult to use and difficult to maintain. Programs with a single purpose are easier to improve as better algorithms or interfaces are developed. In UNIX, small utilities are often combined to perform more demanding tasks when the need arises, rather than trying to anticipate a user’s needs in one large program.
• Reusable Components: Make the core of your application available as a library. Well-documented libraries with simple but flexible programming interfaces can help others to develop variations or apply the techniques to new application areas. Examples include the dbm database library, which is a suite of reusable functions rather than a single database management program.
• Filters: Many UNIX applications can be used as filters. That is, they transform their input and produce output. As you’ll see, UNIX provides facilities that allow quite complex applications to be developed from other UNIX programs by combining them in novel ways. Of course, this kind of reuse is enabled by the development methods that we’ve previously mentioned.
• Open File Formats: The more successful and popular UNIX programs use configuration files and data files that are plain ASCII text or XML. If either of these is an option for your program development, it’s a good choice. It enables users to use standard tools to change and search for configuration items and to develop new tools for performing new functions on the data files. A good example of this is the ctags source code cross-reference system, which records symbol location information as regular expressions suitable for use by searching programs.
• Flexibility: You can’t anticipate exactly how ingeniously users will use your program. Try to be as flexible as possible in your programming. Try to avoid arbitrary limits on field sizes or number of records. If you can, write the program so that it’s network-aware and able to run across a network as well as on a local machine. Never assume that you know everything that the user might want to do.

What Is Linux?

As you may already know, Linux is a freely distributed implementation of a UNIX-like kernel, the low-level core of an operating system. Because Linux takes the UNIX system as its inspiration, Linux and UNIX programs are very similar. In fact, almost all programs written for UNIX can be compiled and run on Linux. Also, some commercial applications sold for commercial versions of UNIX can run unchanged in binary form on Linux systems.

Linux was developed by Linus Torvalds at the University of Helsinki, with the help of UNIX programmers from across the Internet. It began as a hobby inspired by Andy Tanenbaum’s Minix, a small UNIX-like sys...