Unix Introduction

UNIX is a computer Operating System which is capable of handling activities from multiple users at the same time.UNIX commands can often be grouped together to make even more powerful commands.

Parts of Unix Operating System:

The UNIX operating system comprises three parts: The kernel, the standard utility programs, and the system configuration files.

kernel:

The kernel is the core of the UNIX operating system. Basically, the kernel is a large program that is loaded into memory when the machine is turned on, and it controls the allocation of hardware resources from that point forward.

Standard utility programs

These programs include simple utilities like cp, which copies files, and complex utilities, like the shell that allows you to issue commands to the operating system.

System configuration files:

The system configuration files are read by the kernel, and some of the standard utilities.

Types of UNIX:

There are many different versions of UNIX.
Sun Solaris
GNU/Linux
MacOS X

An UNIX Terminal window will then appear with a % prompt, waiting for you to start entering commands.

UNIX was originally developed at Bell Laboratories as a private research project by a small group of people. Read all about the history of its creation.

we shall use the following typographical conventions:

Characters written in bold typewriter font are commands to be typed into the computer as they stand.

Characters written in italic typewriter font indicate non-specific file or directory names.

Words inserted within square brackets [Ctrl] indicate keys to be pressed.

Don't forget to press the [Enter] key: commands are not sent to the computer until this is done.

The UNIX operating system is made up of three parts; the kernel, the shell and the programs.

The kernel

The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.

As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile (which has the effect of removing the file myfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.

The shell

The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).

Filename Completion - By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.

History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.

Listing files and directories

ls (list)

When you first login, your current working directory is your home directory.

% ls (short for list)
The ls command lists the contents of your current working directory.

ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with UNIX!!!

To list all files in your home directory including those whose names begin with a dot, type
% ls -a

mkdir (make directory)

We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type

% mkdir unixstuff

To see the directory you have just created, type
% ls

Changing to a different directory

cd (change directory)
The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.
To change to the directory you have just made, type
% cd unixstuff
Type ls to see the contents (which should be empty)

In UNIX, (.) means the current directory, so typing
% cd .
NOTE: there is a space between cd and the dot
means stay where you are (the unixstuff directory).
This may not seem very useful at first, but using (.) as the name of the current directory will save a lot of typing, as we shall see later in the tutorial.

(..) means the parent of the current directory, so typing
% cd ..

Pathnames
pwd (print working directory)
Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type % pwd