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INTRODUCTION TO LINUX SHELL AND SHELL SCRIPTING

 

If you are using any major operating system, you are indirectly interacting to shell. If you are running Ubuntu, Linux Mint or any other Linux distribution, you are interacting to shell every time you use terminal. In this article I will discuss about linux shells and shell scripting so before understanding shell scripting we have to get familiar with following terminologies:

  • Kernel
  • Shell
  • Terminal

 

What is Kernel

The kernel is a computer program that is the core of a computer’s operating system, with complete control over everything in the system. It manages following resources of the Linux system –

  • File management
  • Process management
  • I/O management
  • Memory management
  • Device management etc.

It is often mistaken that Linus Torvalds has developed Linux OS, but actually he is only responsible for development of Linux kernel.

Complete Linux system = Kernel + GNU system utilities and libraries + other management scripts + installation scripts.

 What is Shell

A shell is special user program which provide an interface to user to use operating system services. Shell accept human readable commands from user and convert them into something which kernel can understand. It is a command language interpreter that execute commands read from input devices such as keyboards or from files. The shell gets started when the user logs in or start the terminal.

Lightbox

 

                                                                                      Linux Shell

 

Shell is broadly classified into two categories –

  • Command Line Shell
  • Graphical shell

COMMAND LINE SHELL

Shell can be accessed by user using a command line interface. A special program called Terminal in linux/macOS or Command Prompt in Windows OS is provided to type in the human readable commands such as “cat”, “ls” etc. and then it is being execute. The result is then displayed on the terminal to the user. A terminal in Ubuntu 16.4 system looks like this –

 

                                          linux command line

In above screenshot “ls” command with “-l” option is executed.
It will list all the files in current working directory in long listing format.
Working with command line shell is bit difficult for the beginners because it’s hard to memorize so many commands. It is very powerful, it allows user to store commands in a file and execute them together. This way any repetitive task can be easily automated. These files are usually called batch files in Windows and Shell Scripts in Linux/macOS systems.

GRAPHICAL SHELLS

Graphical shells provide means for manipulating programs based on graphical user interface (GUI), by allowing for operations such as opening, closing, moving and resizing windows, as well as switching focus between windows. Window OS or Ubuntu OS can be considered as good example which provide GUI to user for interacting with program. User do not need to type in command for every actions.A typical GUI in Ubuntu system –

                                                      GUI  Shell

There are several shells are available for Linux systems like –

  • BASH (Bourne Again SHell) – It is most widely used shell in Linux systems. It is used as default login shell in Linux systems and in macOS. It can also be installed on Windows OS.
  • CSH (C SHell) – The C shell’s syntax and usage are very similar to the C programming language.
  • KSH (Korn SHell) – The Korn Shell also was the base for the POSIX Shell standard specifications etc.

Each shell does the same job but understand different commands and provide different built in functions.

 

 

PRESENTED BY –

Subhasmita Pattnaik( Lect. in Csc)

Subhasmita Pattnaik