Concepts

• Operating System
• Kernel
• Shell
• Utilities
• Command
• File
• Directory
• Folder
• Editor
• Scripts

Operating System

• An operating system is the collection of software that allows you to use a computer
• It has three components
  • Kernel
  • Shell
  • Utilities

Kernel

• All interaction with hardware goes through the kernel
• When a program need read a file ...
• create a directory ...
• or use any piece of electronics on the computer ...
• it must do this using the kernel
• The kernel is a hardware traffic cop
• It prevents one program from interfering with another
• For example, only one program can write to a file at any point in time
• The kernel starts working when the computer turns on ...
• and stays working in memory until the computer shuts down
• No program can run without help from the kernel

Shell

• The shell is a program that lets you run other programs
• The shell give you the command line

Bash

• There have been many different Unix shells down through the years
• The shell we will be using in this class is Bash
• The name comes from the humorous acronym Bourne again shell
• The original Unix shell was written by Steve Bourne
• Bash is probably the most popular Unix shell

Utilities

• Utilities are small programs that allow you to manage the resources on the computer
• They allow you do to things like create a directory ...
• copy a file ...
• move a file from one place to another ...
• or work with text files
• Examples of Unix utilities
  • ls
  • cd
  • mv
  • sort
  • grep

Command

• A command is program run from the command line
• The program could be
  • A binary file original written in C like ls
  • A program written in a scripting language like bash or python3
• In general, each command is the name of an executable file somewhere on the hard disk
• The program name can be followed by options and arguments
• Options make the program run slightly differently than usual
• Example - ls -l
• Arguments tell the command what to act upon
• Example - ls it116

File

• A file is linear arrangement of data on some electronic device
• Linear means it is one dimensional
• It has a beginning and an end
• Files live on hardware like
  • Hard drives
  • Servers
  • Thumb Drives
  • SSD Devices
  • CDs

Directory

• A directory is a container that holds files and other directories
• It is used to organize data on an electronic device
• Directories are sometimes called folders

Folder

• Another name for a directory

Editor

• An editor is a Unix program than can create and change a text file
• Examples of Unix editors
  • nano
  • vi
  • emacs
• Text files are files that only contain characters
• They contain no formating information
• Editors are important in Unix because text files are used to customize your environment

Scripts

• Scripts are text files containing small programs
• Because the computer does not understand text, scripts must be run using an interpreter program
• In this course we will write shell script in Bash
• Scripts cab also be written in interpreted languages like pyhton or perl