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In this lesson you're going to learn some very important details when it comes to getting started with

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shell scripting.

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You're going to learn about shebang comments shell built ins variables and more so there's really a

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lot in this first lesson.

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If you have shell scripting experience in those topics seem basic are old hat to you.

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Just be patient with me bear with me for just a moment.

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We'll be getting to some new material for you soon enough.

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You can either follow along right now with me or wait until the practice exercise.

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That's coming up very soon in the practice exercise you'll get to apply the concepts that you learn

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in this lesson.

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The first thing I'm going to do is open up a terminal on my local machine here I am on my Mac and this

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process is the same whether you're using Mac or Linux or Windows as your primary OS.

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Now what I want to do is move into our working directory which is shall class.

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So I'll S.D. into shell class and now I'm going to make a new directory that's going to house our vagrant

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project for a virtual machine that we're going to create and work on for the next few sessions and for

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the first couple of practice exercises.

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So we'll get into the show class director here we'll create local users make sure local users will change

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into that directory.

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The reason why I'm calling this directory local users is that we're building toward creating a script

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that is going to create local users or users that are local to a system.

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Later on in the course we'll be creating a script that will add remote users or users to systems other

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than the one that your script is executing on.

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But for now we're focusing on local users.

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Now let's create the vagrant file with vagrant Annette and we'll specify the class image that we're

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using

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in order to run and execute the shell scripts that you and I are going to be creating we need to be

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inside the virtual machine in side the Linux system that we've created.

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So we'll get in there by connecting over SSA to a run vagrant SS age and that will connect us to the

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virtual machine that we just created.

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Let's change into the forward slash vagrant rectory with seedy forward slash vagrant and press enter.

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I'm going to run LSA dash l here and that is a long listing format of the Ellis command the dash L and

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it just displays the files that are in the directory.

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Now it's important to note that we have the vagrant file so on our current system in forward slash vagrant.

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It's the same as our local system.

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As in your home directory shall class local users.

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So as you can see here this is my home directory.

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It mounted slash vagrant to this local system.

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So whatever we create inside the VM and the vagrant directory ends up on our local machine in that local

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user's directory and vice versa.

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So here you really have a choice to make.

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You can either edit your scripts inside the virtual machine using nano emacs or vim or you can use the

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editor on your local system.

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So for me I'm going to use vim because that's my favorite editor.

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I've done a class on it.

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I could talk hours and hours about them.

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I totally love it.

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So that's what I'm going to do.

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But I will demonstrate what it looks like from the other side here so I'm going to go ahead and start

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creating the script.

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I'm going to use my vim command vim and I'm going to name the script L user dash demo 0 one dot S H.

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Now I want to point out here that file names with shell scripts really don't matter.

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We'll get into what does matter in just a second.

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So by convention shell scripts can end in dot s h but they're not significant.

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The file extension is not significant like it is for example on windows when something has a dot exec

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file extension.

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That's not the case on Linux.

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We could name this anything we could just name it our user test demo or one or DSH or Bob or Fred or

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any name that is a valid file name and that will work as a shell script.

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So let me edit this file real quick and I'm just going to put a little bit of information in here.

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A pound sign an exclamation mark Ford slash been 4 slash bash and I'm going to save my changes here

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and what I'm going to do to show you what happens with the file sharing I'm just going to do an Alice

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in this directory.

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You can see that the El user Desdemona Wanda s each file was created.

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But I'm going to open up that file in an editor on my local MAC system and so I'm going to use Adam

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in my case.

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So here I have that same file open in the Adam Ed but as you can see it's in the shell class.

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Local users.

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So that's where it's at.

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On your local system.

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I'm just gonna add another line of text here.

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I'll say hello from the main O S and I'm going to save my changes now if I go back to the terminal where

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I'm logged into the virtual machine and look at this file those changes will be there.

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Let me go ahead and just close up this file to make sure nothing is going to interfere with that will

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go back to our terminal and if we display the contents of that file El user demo one that S H.

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You can see that this new line of text has been added so that's what I'm talking about your decision

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of whether to edit from your local machine or whether to edit inside the virtual machine.

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Again I'm going to primarily edit inside the virtual machine here and I'm going to get back into that

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file vim El user dash demo 0 1 and by the way El user is just my personal shorthand for local user.

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So that's what that's about.

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Now let's talk about this very first line in this shell script.

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It's a pound sign followed by an exclamation point and then a path to bash which is forward slash Ben

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or slash bash.

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This is called a shebang.

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The reason why it's called a shebang is the pound sign is sometimes called a sharp.

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If you've ever played music or read music you'll know that the pound sign looks very very similar to

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a sharp sign of music.

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So a lot of people call the hash mark or hash symbol or pound sign.

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Sharp as far as the exclamation point.

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Slang for that is bang.

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So we have sharp bang but an inexact contraction of those two words is shebang.

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So that's where shebang comes from.

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And you want to start out each shell script with the shebang.

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Sharp bang and then a path to the interpreter.

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So what will happen when you execute this script is that the commands inside the script will be interpreted

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by 4D slash band forward slash Bash.

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Now if you had put in another interpreter for example let's say user bean Python or band Ruby or whatever.

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Now that's a ruby script but we're doing shell so we'll keep it as bash.

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So really what happens is when you execute this script Ben Bash we'll get executed and the file name

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actually gets passed to that script and what happens is bash then executes everything in this file.

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I'll demonstrate that later in the course by showing the process table and so on.

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But for now just know that the first line the shebang determines what is going to execute the commands

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listed in the file that you're creating.

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If you do not supply a shebang and specify an interpreter on the first line of the script the commands

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in the script will be executed using your current shell.

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And that may not be what you want.

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For example if you have some bash specific items in your shell script and you happen to be using the

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CSA each shell when you execute it then you're gonna end up with some errors.

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And this is really important especially if you're working with the team you're writing a shell script

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and you have no idea what Shell the other person will be using when they execute this.

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So you want to be very explicit use the shebang and make sure you specify which interpreter that you

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want to use for the script.

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So I want to remove this line we added in the other editor and what I like to do at the top of my shell

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scripts is to give a goal or comment about what's going to happen when the shell script is executed.

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So when you start a line with a pound sign it's actually a comment.

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Comments are not executed.

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They're just simply there for us humans only with the exception of course of the first line which is

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a special line.

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But in all other cases that information there is just for us humans.

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So we can put anything after the pound sign after the comment and it's not going to affect the functioning

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of our program.

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And so here at the very top of the script I'm going to tell what it does

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so this script just displays various information to the screen.

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That's all this script does.

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And so that's what I'm going to put at the top of the file.

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Now when you start making very long and complex scripts and you come back to it a year later or someone

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else looks at it and they're not sure what it does.

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Just having a few notes at the top of the script can really help someone out there.

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I'm going to add another comment.

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We're going to say what we want to do is display the text.

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Hello and we're going to use a command called Echo and then supply the text we want to display to the

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screen which is helo and we'll put that in single quotes.

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I'm going to save my changes and then I'm going to exit out of the editor.

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So just a minute ago I talked about file extensions and how they weren't relevant.

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Now what is relevant is an execute bet on the script.

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Now hopefully by the time you've got to this course you understand file permissions but very quickly

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I'm going to do a quick review of them.

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We'll just take a look at our previous LSA output here as a demonstration.

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So these are w characters are stands for read W stands for right and what goes here is X for executable

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and there will be three sets of these three permissions.

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So we have RW dash our dash dash dash dash.

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So the first three characters here represents the permissions of the owner of the file.

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The next three characters represents the permissions that are granted to the group in the file.

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In the last three characters here represent the permissions that everyone else on the system has to

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this file.

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So in this case the vagrant user.

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This is the user as read write permissions.

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The vagrant group has read permissions and then everyone else who is not the vagrant user or in the

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vagrant group has read permissions to this file.

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What we want to do is add execute permissions so that I you and anyone else can actually execute this

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file and how we do that is with command.

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So due to mod 7 5 5 0 user demo or 1 And now let's look at the permissions now they are RW X which is

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read write execute read execute for the group read execute for everyone else that's not user or the

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owner of the file and in the vagrant group.

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So what this does is if you have read permission obviously you can look at the contents of the file

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if you have right permission that means you can change the contents of the file and if you have X permission

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that means you can execute the file.

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Typically we want to rewrite and execute for ourselves and read and execute for other people.

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By the way if you can't read the file then you can execute it because you can't see the contents that

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are going to be read in by the interpreter and execute it and so on.

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So typically the default permission you want to put on your shell scripts is 7 5 5.

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So really quickly review where does this 7 5 5 come from.

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Well read you can think of as 4 right as 2 and execute as one and you add those together.

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So 7 is four plus two plus one which is read plus write posts execute so 4 to one is 7 and that is for

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the owner of the file 5 is read which is 4 plus 1 execute.

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So that's 5.

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And that is for the group.

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So this corresponds to this middle set here.

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5 again is the same thing 4 plus 1 is 5 and that is for everyone else.

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So if this is a little bit confusing for you or you don't want to remember the specifics.

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Just remember that the default permission we're going to be using is to mod seven fifty five on the

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name of your script.

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Okay.

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So now we have a script.

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It's executed.

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Also how do we execute that script.

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Well the first thing you want to do is type in period forward slash and the name of the script and then

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press enter.

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So the output of this script is simply the word hello.

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And that is because of the command echo Hello that we placed in the script.

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Now I want to point out here that dot represents this directory.

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So for example if we did seed space dot we wouldn't go anywhere we would still be in the same directory.

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Dot dot represents the parent directory.

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So if we did see dot dot we move to the directory above the directory we were in.

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Let me go back in the vagrant directory so dot is this directory.

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And as you can see the forward slash is the directory separator so dot forward slash means this directory

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is dot forward slash is a directory separator and then the name of the script is the file.

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So that's how you execute a file in your current directory.

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Dot forward slash and then the name of the file.

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This is equivalent to the full path.

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So we could actually run or slash vagrant l user demo 0 1 and hit enter as well.

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And again the reason why this dot slash works is because dot represents the current directory which

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is a Ford slash vagrant.

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And then we specify a Ford slash which is the same as this Ford slash and then the name of the file

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which is the same as the name of this file.

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So that's why that works so that's how you do it.

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So just remember tomorrow some 55 dot Ford slash and then the name of the file by the way we could have

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named this file anything again dot DSH doesn't matter as a matter of fact I'm going to rename the file

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really quick l user demo I want to Jason it's a matter of fact that's a typo I even misspelled my own

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name incorrectly but it doesn't matter I'm an executed anyway dot org slash J a o s n and we get the

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same results I'm going to move that back

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let me show you what it looks like when you don't have the execute bit set let's just use the touch

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command to create an empty file that's what touch does touch either creates an empty file if one doesn't

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exist or it updates the lacks access timestamp of a file do an Alice here in this directory.

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So we have blood out S H There is no executable bit set on it so if we do dot forward slash Blau S H

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and hit enter we get permission denied because we do not have execute permission on that file so that

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is what's gonna happen when you don't have the proper permissions set so again make sure you do trim

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on seven fifty five in your file and you'll be good to go let's continue working on our script we'll

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use vim and edited our file here.

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So let's look at this echo command I kind of glossed over it to just get it started here and show the

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execute permissions and talk about file extensions and that sort of thing.

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So the echo command just displays whatever is passed to it.

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Well where does echo come from.

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Well let's check it out back on the command line Echo is actually a shell built in.

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That means it's a command that's built within the shell it doesn't require any external programs to

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execute it's really just part of bash.

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So how do we know it's a shell built in.

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Well you can use that type command which is also a shell built in to show you if it's a shell built

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in or not.

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So if you do type space the command you're interested about which we are interested in echo it says

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Echo is a shell built in.

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So if you want to see all instances of Echo on your system you do type dash a for all and then type

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echo.

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And so it listen in the order that they will execute.

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Echo is a shell built in.

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So really that's what's going to execute when you type echo we'll just type echo now on the command

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line echo Hello.

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Just like we had on our script and press enter and the shell built in is what is executed.

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Now we can force the execution of this by using the full path user bean echo and then pass something

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to it to display what you want to do is actually anytime there is a shell built in to use the shell

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built in.

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So don't specify the full path.

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Just use echo and it's a little more efficient because again it's built into the shell the shell doesn't

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have to request an external program to do some extra processing and what have you.

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So just use the shell built in when it's available.

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Another advantage of using shell built ins is that it's a more portable for example if the echo command

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is on Ben echo and some systems and it's on user been in another system then you might run into some

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issues there.

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But if you use the shell built in you avoid all of that so you can kind of think of these built ins

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as free stuff you get by using bash and there's more than just these built in commands and functions.

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There are built in variables and all sorts of things which we'll be getting into soon enough.

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By the way if you want to get help on a shell built in use the help command so we'll do help echo and

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a lot of that information scrolled off our screen quickly someone to pipe it to less it's a pager so

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we can page up and down to this output I'm going to pipe it to less it enter and it says echo rights

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arguments to standard output display the arguments on the standard output followed by a new line.

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So that's what the echo built in does.

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Let's look at an example of a command that is not a shell built in one command that comes to mind as

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uptime so uptime just displays how long this system that you're logged into has been up will do type

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dash a pass and uptime to that.

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This is uptime is actually user been uptime that's what it gets executed when you run uptime.

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So if you run help uptime you're not gonna get any help because it's not a shell built in.

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However if you wanted to get help on uptime you would use the man command which is short for man pages.

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So man or manual man uptime and press enter.

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So that's how you get information on how to use commands that are not part of shell built ends and we'll

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be looking at man pages along the way as well as help or built in Shell commands.

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By the way to exit out of man type Q And it's the same way with less if I didn't mention that as well

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you just type Q to exit that page nation system there as well remembered that a shell script just executes

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ever command inside that script just as if you were typing it on the command line.

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So if we look at the contents of our script here if we were to do this pound space display low and press

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enter nothing happens because the pound sign is a comment and comments aren't executed and if we type

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in the next line in the script echo hello and press enter.

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Then we get Hello displayed to the screen.

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And that's exactly what happens when we execute the script.

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By the way this simple echo command can come in really handy when you're debugging or writing scripts.

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You can use it to show exactly what is going on inside the script along the way.

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Now let's get back to editing the script let's assign a value to a variable

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let's call this variable word.

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We'll follow that with an equal sign.

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A single quote script and end it with a single quote.

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I'm going to save my changes now variables are simply storage locations that have a name.

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In this example the name is word you can think of variables as name value pairs.

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So if we were to access the variable of word the value that would be returned would be script.

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Unlike some other programming languages when you're creating variables you don't have to specify its

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type whether it's a string or an integer or anything like that you just assign it a value.

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By the way I want to point out that it's very important that there is no space in between the equal

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sign.

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So it's the variable name followed by an equal sign without any space.

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Again without any space then the assignment in this case we're assigning a string and strings are enclosed

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in quotation marks either a single quotation marks or double quotation marks.

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By the way I recommend that you use a descriptive name for your variables although it's not required.

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This simply just makes the script easier to read.

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Now think about someone else who's going to be reading the script or maybe even yourself if it's a year

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later or a long time after you've originally written the script.

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It would be easier for you to tell what's going on if the variables had meaningful names.

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Now as a quick aside I want to tell you about someone I worked with whose last name started with Z and

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so everything he created contained a Z.

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If you looked at his home directory he had a bunch of shell scripts one shell script was name Z.

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The next shell script was named Z.

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The next shell script was named Z and there was a shell script.

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Ze one one name ze to one name.

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Xie xie xie xie 1 1 2 etc. just went crazy like he had no imagination other than the letter Z.

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And then when you opened up one of his scripts and looked in them all the variables were the same.

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Z equals blah ze 1 equals blah Z was blah.

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He was the only person that had any kind of clue of what was going on when his scripts because they

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were almost impossible to read.

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So again using something like that works it's just not recommended by the way there are some rules around

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variable names variable names can contain letters digits and underscores and they can start with letters

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or underscores but they can not start with a digit.

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So for example word is a valid variable name.

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Word 1 is a valid variable name underscore word is a valid variable name.

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00:22:28,580 --> 00:22:33,470
However 3 word is not a valid variable name.

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Also you cannot use dashes so something like this a dash word is not a valid variable name it's invalid

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00:22:41,420 --> 00:22:42,650
you can't use that.

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00:22:42,830 --> 00:22:46,460
One more example would be an at sign you can't use that as well.

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E at male equals something is not going to work.

305
00:22:51,820 --> 00:22:54,820
Let me get rid of these example names here.

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Now that we've assigned a value to our variable let's go ahead and use that variable

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00:23:07,880 --> 00:23:10,330
so we'll just to echo space.

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Double quotation marks.

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Dollar sign.

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The variable name which is a word in end it with a double quotation mark so when you reference the variable

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by name you get its value back.

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Now to do that you have to proceed.

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The variable name with a dollar sign.

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So when we want the value of word we use dollar sign word.

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Now you may have noticed that in the previous echo statement I used single quotes but in this echo statement

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I use double quotes single quotes prevent the expansion of variables.

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So if you want echo to display exactly what you specify put it in single quotes if you want variables

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to be interpreted make sure that you use double quotes.

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By the way we're just using the echo shell built in for now.

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But this concept of single quotes and double quotes apply to other commands as well to say that another

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way it's not because we're using echo that this expansion happens with double quotes and it doesn't

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with single quotes it's the quote to themselves that is causing this expansion or not.

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And then you can use this functionality with other commands not just with Echo.

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So let's execute the script and see what happens okay.

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We get Hello which is from Echo Hello.

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Then we set the word variable to equal script and then we displayed that word variable which actually

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in turn displays the word script by the way you can do what I'm doing here.

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As far as your workflow goes which is to open your editor edit the file exit your editor and then execute

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the script.

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Another thing you could do is actually open up a new terminal window connect to the vagrant system get

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into that directory and then execute that script with the other terminal so you just switch back and

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forth between terminals versus entering and exiting your editor all the time.

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Just use whatever method works best for you.

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For now for the rest of this lesson I'm just going to edit the script exit out execute the script and

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so on.

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So let's return to editing our script add a comment here of what we're about to do

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okay we're putting dollar word which is our variable inside single quotes.

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Now let's see what effect that has.

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00:25:34,560 --> 00:25:40,200
So as you can see using Siegel quotes displays exactly what is in the single quotes it doesn't do any

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expanding or interpreting of the variables.

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It's exactly what you specify.

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So just keep that in mind if you're using variables.

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Use double quotes if you want to be very specific and make sure that nothing gets changed use single

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quotes.

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Okay let's do some more editing here

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so you can use variables with hard coded text.

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00:26:09,460 --> 00:26:12,550
So here we have some text that we just manually typed in.

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This is a shell and then we use a variable which has dollar words so we want the value of that variable

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to be returned.

350
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Let's exit out and execute the script and see what happens

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so it gets interpreted and the output is this is a shell script.

352
00:26:46,490 --> 00:26:51,980
You can also enclose the variable name in curly braces and perceive the opening brace with a dollar

353
00:26:51,980 --> 00:26:52,760
sign.

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00:26:52,760 --> 00:26:54,490
So the syntax is dollar sign.

355
00:26:54,500 --> 00:26:59,370
Opening curly brace in the variable name followed by a closing curly brace.

356
00:26:59,450 --> 00:27:04,490
By the way when you're reading scripts written by others you'll see both types of syntax being used.

357
00:27:04,520 --> 00:27:09,890
You'll see the dollar sign with a variable name as well as the dollar sign including the braces in the

358
00:27:09,890 --> 00:27:11,000
variable name.

359
00:27:11,000 --> 00:27:19,700
Now let's execute our script and see what happens so we get the same exact output as the preceding echo

360
00:27:19,700 --> 00:27:20,330
command.

361
00:27:20,360 --> 00:27:30,020
It's we're just using the different syntax.

362
00:27:30,070 --> 00:27:34,180
Now if we want to append text to the variable we have to use this dollar sign.

363
00:27:34,180 --> 00:27:35,320
Brace syntax.

364
00:27:35,530 --> 00:27:36,690
Let me show an example.

365
00:27:43,460 --> 00:27:50,860
So if we want to append AMG directly after the output of the variable we have to use the curly braces.

366
00:27:50,930 --> 00:27:57,920
Otherwise bash doesn't know that the variable is actually word W O R D and that the part that's not

367
00:27:57,920 --> 00:27:59,390
the variable is I N G.

368
00:27:59,390 --> 00:28:05,960
It has no way of knowing that unless you use the braces to separate the variable from the preceding

369
00:28:05,990 --> 00:28:07,430
or following text.

370
00:28:07,430 --> 00:28:11,090
Now let's execute this.

371
00:28:11,300 --> 00:28:13,790
Says scripting is fun again.

372
00:28:13,790 --> 00:28:20,680
Script is what was stored and the word variable i n g is what we card coded in the echo statement there.

373
00:28:24,420 --> 00:28:28,530
So let's demonstrate how not to append text to a variable I was just talking about this.

374
00:28:28,530 --> 00:28:36,490
Let's do this.

375
00:28:36,530 --> 00:28:43,480
So this is not gonna work echo dollar sign a word IAG is a fine again.

376
00:28:43,530 --> 00:28:49,620
BASH doesn't know that high energy is not part of the variable name by the way I didn't necessarily

377
00:28:49,620 --> 00:28:55,910
mention this but by convention not by rule or syntax variables are in all uppercase.

378
00:28:55,920 --> 00:28:59,220
That's why you used uppercase word as a variable name.

379
00:28:59,280 --> 00:29:03,960
And that way you can typically easily spot what is a variable and what is not.

380
00:29:03,960 --> 00:29:11,570
However since that's only a convention or a best practice and it's not enforceable by syntax then bash

381
00:29:11,580 --> 00:29:15,660
isn't going oh I N G is lowercase so therefore it's not part of the variable name.

382
00:29:15,660 --> 00:29:21,210
No that's not how it works you can actually use lower case variables and some people do so this will

383
00:29:21,270 --> 00:29:22,070
not work.

384
00:29:22,080 --> 00:29:22,910
Let's prove it here.

385
00:29:25,570 --> 00:29:29,170
You get blank is fun for the last bit of output.

386
00:29:29,260 --> 00:29:35,850
That's because dollar word IAG that variable doesn't exist so it doesn't expand to anything so there's

387
00:29:35,860 --> 00:29:36,870
nothing there.

388
00:29:37,060 --> 00:29:38,560
And it displays nothing.

389
00:29:38,800 --> 00:29:43,180
And that was followed by a space is space fun exclamation point.

390
00:29:43,210 --> 00:29:45,760
So that is what it gets displayed on the screen.

391
00:29:45,760 --> 00:29:47,340
Space is space fun.

392
00:29:47,350 --> 00:29:48,210
Exclamation point.

393
00:29:50,910 --> 00:29:57,540
Now let's create another variable for a script here.

394
00:29:57,580 --> 00:30:00,760
We're going to name this variable ending.

395
00:30:00,760 --> 00:30:06,070
Again we're going to use all uppercase letters because that is the convention or best practice not required

396
00:30:06,100 --> 00:30:07,870
but that's how we're going to do it.

397
00:30:07,930 --> 00:30:11,040
We're not going to use spaces because that will cause an error.

398
00:30:11,050 --> 00:30:13,480
So we want to make sure there are no spaces here.

399
00:30:13,480 --> 00:30:19,300
We're going to use single quotes and type in E D and close it was single quotes because we're not doing

400
00:30:19,300 --> 00:30:21,250
any variable expansion here.

401
00:30:21,250 --> 00:30:26,210
We're just doing a strict assignment of E D to this variable.

402
00:30:26,230 --> 00:30:29,020
Now let's combine these two variables that we've created

403
00:30:41,470 --> 00:30:45,130
so as you can see we use this dollar sign brace syntax.

404
00:30:45,130 --> 00:30:51,550
So this variable of word will get interpreted and then dollar sign ending here will get interpreted

405
00:30:51,550 --> 00:30:52,490
as well.

406
00:30:52,540 --> 00:30:59,230
So we'll get this is script and this should expand to add E.D. here.

407
00:30:59,230 --> 00:31:01,810
So let's prove this by executing it on the command line.

408
00:31:04,150 --> 00:31:09,790
Sure enough we get this is scripted because the word variable contains the value of script and the ending

409
00:31:10,090 --> 00:31:16,040
variable contains the value of E D.

410
00:31:16,040 --> 00:31:26,000
Now let's change the value that stored in the ending variable.

411
00:31:26,030 --> 00:31:34,450
This is called reassignment by the way.

412
00:31:34,660 --> 00:31:39,370
Now we're going to change the value that stored an ending to AI in G.

413
00:31:39,430 --> 00:31:45,690
By the way you can overwrite the contents of the variables just using assignments or these reassignments.

414
00:31:45,700 --> 00:31:51,400
So the first time ending is specified it's equal to E.D. when you access the ending variable.

415
00:31:51,400 --> 00:31:52,960
That's what gets displayed.

416
00:31:53,080 --> 00:31:57,580
But since the scripts are read from the top down just as if you were typing them in at the command line

417
00:31:57,880 --> 00:32:03,360
when you changed the value of ending then anything that follows that will use that new value.

418
00:32:03,460 --> 00:32:13,370
And let's prove that here we'll do echo dollar sign a word dollar sign ending is fun see where our changes

419
00:32:13,370 --> 00:32:17,450
and execute our script so we have scripting is fun.

420
00:32:17,460 --> 00:32:24,510
So word expanded to script the ending since we changed it to i n g span into AMG so scripting is what

421
00:32:24,510 --> 00:32:27,300
you get when you combine word and ending together.

422
00:32:27,390 --> 00:32:33,510
Again we use that special brace syntax so that that's cartel where one variable started and ended as

423
00:32:33,510 --> 00:32:36,410
well as the other variable where it started and ended.

424
00:32:39,430 --> 00:32:41,080
Let's do one more reassignment

425
00:32:46,650 --> 00:32:48,390
will assign s to ending

426
00:33:01,350 --> 00:33:06,290
hey let's save our changes and execute our script.

427
00:33:06,380 --> 00:33:10,370
You were going to write many scripts in this class all right.

428
00:33:10,370 --> 00:33:15,950
This brings us to the end of this lesson in this lesson you've learned a lot you've learned about file

429
00:33:15,950 --> 00:33:22,370
naming file naming conventions how file names don't determine if something is a script or executable

430
00:33:22,370 --> 00:33:22,810
or not.

431
00:33:22,820 --> 00:33:29,150
It's actually the execute bit on the file itself that determines if you can execute it as a script or

432
00:33:29,150 --> 00:33:30,050
not.

433
00:33:30,050 --> 00:33:35,750
You also learned about beings you learned how to use comments effectively create a header in your file

434
00:33:35,750 --> 00:33:36,250
and comment.

435
00:33:36,260 --> 00:33:41,750
The script along the way you learned about the difference between a shell built in versus a normal command

436
00:33:41,750 --> 00:33:42,560
on the system.

437
00:33:42,680 --> 00:33:48,620
How to get help with shell built ends which is to specify the word help followed by the name of the

438
00:33:48,830 --> 00:33:50,180
shell built in.

439
00:33:50,180 --> 00:33:55,130
You also learn that you can get help about general commands on the system using man pages.

440
00:33:55,130 --> 00:34:01,550
So man followed by the command again man and a shell built in will not provide any help but you can

441
00:34:01,550 --> 00:34:05,800
get help from man bash or help and the shell built in.

442
00:34:05,810 --> 00:34:09,860
Finally we talked about variables how to assign them not to reassign them.

443
00:34:09,860 --> 00:34:15,140
We talked about single quotes and how nothing inside single quotes gets expanded or interpreted and

444
00:34:15,140 --> 00:34:21,590
how things since I double quotes to get expanded interpreted such as variables we talked about the two

445
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different syntax as you can use with variables one is just pre spending a dollar assigned to the variable

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name and the other is pre printing a dollar sign and surrounding the variable in braces you learned

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that that second syntax is required if you want to immediately precede or immediately follow that variable

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with some additional data even though using the dollar sign and brace encapsulation method is a best

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practice when working with variables.

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I showed you the other method so that if you see other people's scripts you know what they're doing

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and it doesn't come as a surprise to you.

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Okay that wraps it up for this lesson.