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In this video, we're going to talk

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about how Linux applies a simple

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and modular design philosophy through the use

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of the command line interface and the shell.

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Now, the Linux operating system emphasizes

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a simple user interface in which the user types

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in text commands into a prompt,

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and that way they can interact with the system.

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This differs from the primary visual operating systems,

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like Windows and macOS, which use a graphical user interface

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or G-U-I, known as a GUI.

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In Linux administration,

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one of the most crucial skills is becoming comfortable

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at entering text commands using the command line interface,

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also known as the CLI.

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Now, the CLI is a text-based interface

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between the user and the operating system

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that accepts input in the form of typed commands.

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A command prompt is presented to the user,

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and the user enters a command to interact

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with the system in a variety of different ways.

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Developers and administrators often use

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the command line interface,

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whereas regular users will like to rely

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on a graphical user interface, or GUI, instead.

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Many distributions though, especially the ones used

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for servers, do not come with a graphical user interface,

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but there are many different GUIs

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that are developed that can be installed

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on top of Linux after the fact too.

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So throughout this course, we're going to focus primarily

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on using the command line interface

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because as a system administrator,

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this is where you're going to spend a lot of your time.

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Now, in addition to the command line interface,

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we have something known as the shell.

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Now, a shell contains the core portion

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of the operating system, referred to as the kernel,

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and it permits the user to pass commands

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and information to that kernel.

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The kernel is also able to respond back

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to the user through that shell.

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The shell can be thought of as an interpreter

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between the humans and the kernel of the operating system.

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Linux users are going to issue commands to the shell

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in order to tell the operating system

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what they want it to do.

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The operating system will then respond back

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to the user with the results of the command.

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A shell can be implemented as either

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a command line interface or a graphical user interface.

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Like most things in Linux,

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you can actually choose which shell you want to use

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within your command line interface too.

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For this course and the exam,

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we're going to focus on the Bash shell.

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The original Unix shell was called the Bourne shell or SH.

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Although it's still available on some Linux systems,

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it has been virtually replaced

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on most systems by the Bourne-again shell

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or B-A-S-H, known as bash.

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Virtually every Linux distribution will use

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this shell as the translator

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between the user and the system by default.

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Now, it is possible to install and use other shells

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in Linux though, if you want to, things like Korn,

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the Z shell and the TC shell are all popular as well.

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Now, when you're using a shell, you need to make sure

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you're using the proper syntax for that shell.

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Syntax is the proper way of structuring a command

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and any supporting information.

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For example, in English, we all understand that

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when I make a statement like, "I want some water,"

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I am using the subject I.

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I'm using a verb, what, and an object, water,

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but if I was speaking a different language,

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the syntax here might change.

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For example, Yoda from Star Wars likes

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to follow a more Japanese style of syntax,

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and he says, "water, I want," which is object,

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then subject, then verb.

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Now, either of these isn't right or wrong,

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but it's right or wrong based on the syntax being used.

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So Yoda uses a different syntax

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than we do in the English language.

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Now, many command line interfaces have their own unique ways

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of entering in information or having a different syntax.

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It's important for you to understand the syntax

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for the shell you're going to be using.

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Otherwise, you're not going to be able

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to effectively communicate with that interface.

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Again, in this course, we're going to be focusing solely

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on the Bash shell syntax.

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Now, the Bash shell syntax contains three main components.

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We have the command, the options to modify the command

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and an argument for the command to act upon.

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It's important to take note here that there are spaces

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in between each of these three components.

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Also, at this point, it's really important

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to remember that the commands entered

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in Bash are going to be case-sensitive.

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So if I wanted to create a copy of a text file named Jason,

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and I wanted to make it called Dion,

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I could use the command cp -i Jason.txt Dion.txt.

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Now, what I just told the command here to do is

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to use the copy command or CP,

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and I want to do that using the modifier option of -I.

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This tells the shell to warn me before overriding a file,

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then I'm going to perform the action on the two arguments,

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the input file, Jason.txt and the newly created

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output file, Dion.txt.

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Now, if you fail to enter a command in the proper syntax,

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Bash will return an error to you.

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Typically, these error messages are very descriptive

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and will help you understand what Bash expects from you.

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For "command not found" errors,

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this simply means the shell doesn't understand

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the command you've asked it to do.

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For example, if I type CPT instead of CP,

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that's not a command it understands.

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Usually, this occurs whenever you misspell something.

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So always check your commands for typos

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if you're getting one of these errors.

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If you get an error like "no such file or directory" errors,

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this means you need to check

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for typos in the directory, file or path names.

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In my example, the Jason or the Dion files.

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Now, we're going to cover specific commands much more

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in depth throughout this course,

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but for now we just need to understand

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that the command line interface is a place

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for us to interact directly with the shell,

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and the shell requires us to use specific syntax

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when we do that, so it can understand

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the commands we're asking it to perform.