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Shell. What is the shell?

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In this lesson, we'll cover about the shell, how the shell

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work, and how you can run command within the shell, or

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how the environment is set up in a shell.

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So what exactly is a shell?

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Shell is like a container.

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Like you have like a tupperware in your

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home or any kind of container that holds

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your environment your information inside of it.

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It interfaces between users and

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Kernels or operating systems.

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So you have built an operating system,

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and then it has provided a platform for

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you to execute commands. Again, Windows is one

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of the platform, and in Windows operating system,

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when you start up a GUI, you execute commands

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by running, by double clicking on a program.

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So that GUI interface is your shell. In Linux, when

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you don't have a GUI, you are given a terminal

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shell or CLI command that is your shell.

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To find your shell you could run a command like echo dollar

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and zero, that will tell you what shell you are in.

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And you could also get a listing of

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all your shells in your Linux distribution by

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running the command cat /etc/shells.

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Your shell is also inside of /etc/passwd

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that is defined inside of the file.

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In Windows, GUI is a shell, in Linux, KDE

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GUI is a shell, in Linux sh which is shell, bash, etc.

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All these are the shell that is provided to a user.

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Again, we're looking at this diagram, again,

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and we are second from the top.

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You'll see the application that talks to the shell

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and then shell talks to Kernel, and Kernel is

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the one that is telling hardware what to do.

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Let's look at our Linux machine and we'll

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see how we could find our shell.

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Open up a terminal real quick.

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And when you do cat, sorry when you do echo

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dollar zero, it tells you you are in bash.

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So you could look at the available shells that is

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installed in your distribution by doing cat /etc/shells and

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it tells you all the shells that are available.

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And when you look at /etc/passwd, cat /etc/passwd

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and you'll see in my username, which is right here,

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it tells the shell all the way at the end

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that I have a defined shell which is /bin/bash.

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I could change that shell if I want

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to, to a different shelf, but I try

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to keep it consistent with other users.

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So that's what the shell does and we'll cover

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the later, in the later lessons, how we could talk to shell to

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create scripts and other things to automate our tasks.

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