UNIX BRIEFLY

Unix OS(Operating System) is a multi-tasking, multi-user operating system that was originally developed in 1969 by a group of AT & T employees.Unix variants include Sun, Solaris Unix, AJX, HP Unix and BSD(Berkeley Software Distribution).
Unix OS is made up of three parts; Kernel, Shell and the programs.
The Kernel: is the hub(heart) of the Operating System. It allocates time and memory to programs and handles the storage of files and communications in response to system calls. It communicates with the hardware and supports handling of tasks like memory management, task scheduling and file management. For instance, as a user I want to remove a file named examplefile, I type in a command rm examplefile (which has the effect of removing the file examplefile). The shell searches the filestorage for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on examplefile. When the process rm examplefile is completed, the shell then returns the UNIX prompt to the user, indicating that it is waiting for further instructions.
The Shell: is the utility that processes user’s request and serves as an interface between the user and the kernel. It uses a standard syntax for all commands and the executable file ends with .sh. They include cp, mv, cat and grep. A shell script is a human-readable script whose interpreter is a shell and is understood by the interpreter as instructions describing the behavior of a program.
Files, Processes and Interactions through Shell Commands
A file is a collection of data that has a name filename. They are created by users using text editors, running compilers etc. Examples are documents(.docx), program text files(.md, .rb, .php), directories, etc.
Basic Shell Commands

Listing directories and files
~ls -l: lists out all files or directories available in a directory.
~whoami: find out who you are
~users: finds out who is logged in
~shutdown: shuts down a unix system properly via the CLI
~reboot: reboots the system.
~halt: brings the system to a stop immediately
~poweroff: shuts down the system by turning off power.
Metacharacters
.profile: The Bourne Shell(sh) initialization script
.kshrc: The Korn Shell(ksh) initialization script
.cshrc: The CShell(csh) initialization script
.rhost: The remote shell config file
For other shell commands that could come handy visit this link.
Thank you for your time.
