CHAPTER 1 - ABOUT UNIX

What is Unix?

Unix is a computer operating system. An operating system is the software that provides the interface between the hardware of a computer system and the applications programs that are used on it. Simply put, the operating system provides the link between the hardware of the computer and the user. Popular operating systems include DOS (used on PCs) and VM/CMS (used on mainframes, now becoming rare). Unix is available on a wide variety of computer systems, including personal computers, workstations, mainframes and supercomputers. It was developed for, and is particularly well-suited to, multi-user systems, but is now also run on 'stand-alone' machines.

A little history

Unix was first developed in the early 1970s at Bell Laboratories in the USA. It was originally developed as a system to be used by the staff in the laboratories, and it was principally intended to provide an operating system that people would enjoy using. It was designed for users who were largely computer scientists, which may explain some of the more arcane and apparently unfriendly features of Unix, such as the obscure sounding command names. AT&T (the owners of Bell Laboratories) made Unix available at nominal cost to academic users, with whom it became popular. This helped to create a market for Unix, at a time when technological changes had themselves created a need for a portable multi-user operating system. As a result Unix began to be adopted by non-academic users in the 1980's as it became commercially available. Several standards are now being worked out, and Unix is steadily becoming the standard operating system in many environments.

What's special about Unix?

Unix has the following advantages: Portability Unix is written in the high level language C. This makes it easy to install on new computing systems. Applications written to run on a Unix system will hopefully run on any Unix system, regardless of the hardware. Popularity Unix is available on many widely-used systems. It is very widely used and it has become the de facto standard for academic users, and for all multi-user applications.

Power

A wide and growing range of applications software is available. Unix provides a range of tools that can be combined and manipulated to perform such a wide variety of jobs that users of the system can very often carry out sophisticated tasks without writing programs in a programming language. Standardisation Although there are many versions of Unix, these are already largely compatible, and official standards are currently being defined.

Different Unix systems

They are many different versions of Unix, as well as some Unix 'lookalikes'. The most widely used are:

System V (distributed by the original developers, AT&T)

AIX (IBM)

Berkeley BSD (from the University of California, Berkeley)

SunOS, now known as Solaris (from the makers of Sun workstations)

Xenix (a PC version of Unix).

Unix features

The kernel and the shell

The Unix operating system consists basically of the kernel and the shell. The kernel is the part carries out basic operating system functions such as accessing files, allocating memory and handling communications.

A shell provides the user interface to the kernel. A number of shells are available on the Unix operating system including the Bourne shell and the C shell. The shell is basically an extensive program that runs all the time that you are logged on to the computer, and provides an interactive interface between the user and the computer functions. The C shell is the default shell for interactive work on many Unix systems. It will be covered in this document.

See chapter 13 below for more details.

Graphical User Interfaces

Graphical User Interfaces (usually written GUIs and pronounced 'gooeys') provide an alternative user interface to shells such as the C shell and Bourne shell.

GUIs provide a replacement to the command line interface based on the use of icons, menus and a mouse. Using GUIs, applications software from different suppliers can have a consistent interface, which reduces the time needed to master new applications.

If you have access to a workstation or a powerful PC with the necessary software, you may wish to attempt to master a GUI, especially if you are already used to using a PC windows environment. You can create shells within a GUI environment and continue to work through this course, as well as having more utilities available to you. Using a GUI will not be covered in this course however, since the lack of a standard means it is not clear which should be taught. Furthermore, the commands and utilities taught here deal with Unix at a more fundamental level than GUI interfaces provide, and what you will learn here will give you an insight into how Unix actually works, give you access to the full power and flexibility of Unix. The skills learned here should be of use in many different applications and environments.

On-line tutorials should be available with GUI implementations and provide an introduction to their use.

Text processing

Standard Unix implementations offer a variety of text editors and formatters.

Editors

It is essential that a Unix user becomes reasonably proficient in the use of at least one editor if they want manipulate text files. Most users nowadays with experience of word-processors prefer a screen editor, and these generally provide the friendliest interface. There are good reasons however for learning to use the Unix line editor, as it's use involves learning a great deal about the way that Unix commands and programs deal with strings, texts, contexts, etc.. In this course we will therefore look in some detail at ex, the enhanced Unix line editor, and at the other text processing utilities that have been built on the basic ex functions. You are recommended to look ahead to the chapter on ex as soon as you have need of a text editor. If you find using ex impractical, use a screen editor. The standard Unix screen editor is vi, but as this is built on ex, you need some knowledge of ex to make use of the majority of it's functions, which are in any case very different from those of a modern editor. Some version of emacs is usually available on Unix systems, and it may be best for you to use this. Emacs is available on other systems, such as DOS, and is a good general purpose editor.

On the other hand, the advantage of using vi is that it is always available in basically the same form on any Unix system, so if you learn vi, you know that you will always be able to use a screen editor on any Unix system. What is more, once you have learned about ex, you will be to exploit some of the power of vi without much extra effort. It is therefore certainly worth having at least a basic familiarity with vi, and many users use it as their preferred editor. The decision about which editors to use and when depends on your own needs and preferences. If you want to use a screen editor straight away, use emacs, or whatever is available on your system. At a later date, a little effort to learn vi could be well rewarded.Further reading: Documentation on vi is available on-line (type man vi) and in the SunOS manuals. There is a prose introduction in chapter 24 of Nishinuma (1987).

If you are using some type of windows program then there will be a simple interactive screen editor (such as textedit with OpenWindows) available with the program, and this will be more suitable than emacs for simple tasks.

Text formatters

Unix has its own text formatters (principally nroff and troff.) and systems will often support other documentation software, such as TeX. Many users will have no use for these, and will prefer to use a word-processor. A short introduction to nroff is given in Chapter 12.