What is UNIX?
The UNIX Operating System
was first designed and developed in the 1960s and since then its constantly growing with consistent development all around the world. The operating system is nothing but a complete package that makes your computer operate properly.
Somewhat similar to Windows OS GUI (User Interface), UNIX also has its own GUI. But most of the UNIX users still prefer using the UNIX shell (Command) prompt for their regular action on UNIX OS, as the UNIX GUI does not have all the functions provided by the UNIX Shell.
Like Windows OS, UNIX is also a multitasking, multiuser and can act as stable system for many servers, desktops and even for laptops too.Types of UNIX
The main types of UNIX
- Sun Solaris
- MacOS X
There are other types too, but they all are similar to each other.The UNIX operating system
The UNIX operating system is made up of three parts; the kernel, the shell and the programs.The kernel
The heart of the UNIX operating system is the Kernel and therefore it is always available into the memory. The main task of this Kernel is to allocate memory and time to different programs running under UNIX. There are other tasks like managing the filesystem (filestore) and giving responses to the system calls.
This Kernel and the Shell are always works systematically with each other. For e.g. If a user types in the command rmdir dirname (which means remove or delete a empty directory), then the Shell locates the script for “rmdir” command and then instructs the Kernel through specific system calls to execute this command on the directory ‘dirname’
The Kernel then does its job, and returns control back to the Shell, which then return the control back to the user by giving them the UNIX command promptThe shell
The Shell is nothing but a command prompt that helps the user to talk to the Kernel and instruct it to execute the required commands. When the system (computer) start and user enters his login access details, the login script verifies the access and loads the Shell for the user. The Shell is also called as the CLI i.e. Command Line Interpreter and its main function are to interpret the commands entered by the user and give them to the Kernel for execution. Shell is nothing but a script or program having its own defined tasks.
The advanced users who are good with the programming skills can modify the current shell and customize it as for their own requirements. They can even run two different Shells (one default and another customized) on one machine.
The most common Shell is the tcsh Shell having features that help users to use UNIX easily. Users normally operate on tcsh Shell by fedding (entering) commands for it.
UNIX Shell has a feature. We will call it as ‘Filename Completion
’, meaning if the user operating on the command prompt types the part of the command or the filename or even the directory name and press the tab key, the ‘tcsh’ Shell will automatically complete the command or filename/directory name for the user. It also has error handling, like if the Shell fails to find or finds more than one command matching the characters typed in by the user, then it will beep and prompt user to enter few more characters for the command or filename/directory name.
The other feature of the Shell is to maintain the list of all command that user had typed in or executed. We will call it as 'Shell History
'. User can make use of this feature to save the typing efforts, as the earlier entered command can be recalled on the command prompt by using the cursor keys available on the keyboard.Files and processes (Tools and Applications)
Everything in UNIX is either a file or a process.
A process is an executing program identified by a unique PID (process identifier).
A file is a collection of data. They are created by users using text editors, running compilers etc.
some examples of UNIX files
Also read: Advantages of Unix/Linux over Windows
- Simple document file (reports, essays etc.).
- A script or program written in high-level or low-level programming languages.
- A executable binary file, containing commands comprehensible directly to the machine and incomprehensible to a casual user.
- A directory file or simply directory, maintaining information about its contents, general files or even other directories i.e. sub-directories.
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