• Table Of Contents

Introduction

History

• UNIX was an open-source, multi-tasking operating system developed by Bell Laboratory, and allowed people to receive a source-code and compiled copy of the same if we'd send them a recording medium.
• Richard Stallman founded Free Software Foundation, and started working on his own GNU (GNU’s Not UNIX) operating system
• GNU/Linux came into the picture, by Linus Torvalds, and at that time, GNU/Linux OS had completed development of major system applications such as compilers, text editors and other such accessories but the Kernel wasn’t cutting edge. Linus’s GNU/Linux used all those GNU utilities as part of his operating system, but had his own kernel based out of UNIX. Later many distributions using Linus’s GNU/Linux came out as well, such as Fedora, Ubuntu, Debian, Slackware etc.
• BSD UNIX was also out there, based out of Bell Laboratories’s UNIX, made by students at UCB, and it has its own different distributions as well, based out of the BSD Unix kernel, such as FreeBSD, NetBSD, OpenBSD, DragonflyBSD etc.
• The main kernel component of MacOS, Darwin, is also based out of BSD UNIX.

Linux desktop environment

• The program which and gives us a GUI is known as an X-Windows System.
• Individual programs responsible for the appearance of the GUI are layered on the top of the X-Windows system, such as: GNU GNOME, KDE (K Desktop Environment), Xfce, Unity, MacOS Aqua GUI etc.

Linux Shell

There could be many ways to interact with the OS, and tell it to do something, some of them being: Graphical user interface (GUI), Touch screen interface, and Command line interface (CLI)

What is it?

• It's a command line interpreter used to parse terminal commands and run programs on a computer. They listen to commands from the terminal and translate the requests into actions by the kernel and programs.
• On the other hand, a terminal is a non-GUI utility which uses the shell to interact with the system.
• A shell has features like program execution, variable& filename substitution, I/O redirection, pipeline hookup, environment control etc.
• Example of Shells: zsh, sh, bash, ksh, Powershell, cmd etc.
• When we open the terminal, the Linux initialises our environment by loading configuration files such as .bashrc, .bash_login, .bash_profile, .bash_logout etc.

Environment variables

<aside> 👉 Basics

</aside>

• Upon opening a new terminal instance, a new shell process having its own set of environment variables is initialised
• Environment variables are variables which come predefined when we start up our shell instance, and also get inherited by its child processes. They are like configuration settings for our shell

#Check all the environment variables for our shell
env

#Define a global variable, but no space should be b/w =
export variableName="value"

<aside> 👉 $PATH

</aside>

• A colon separated list of directory paths that our shell will look through whenever a command is run w/o its absolute path
• We can add new directory to the $PATH environment variables, but it creates an unnecessary security, we should rather utilise the concept of Symlinks.

#Check all the directory defined in the $PATH variable
echo $PATH
/usr/local/sbi n:/usr/local/bin:/usr/sbin:/usr/bin :/sbin:/bin

#Add a new directory to $PATH by editing the .bashrc file, or its equivalent
export PATH='path:$PATH'

>Operators in Linux

Linux Operators

>Data Stream, Piping and Redirection