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Welcome to the exercise walk through.

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This is where you'll get a chance to look over my shoulder if you will and see how I approach this particular

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exercise.

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The first thing I want to do however is just set the stage give me a little bit of background information

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about a situation where you might use this in the real world.

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Let's say that you're a Linux system administrator for growing fast paced company.

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You have a lot of projects and deadlines that you're working on and working toward But you keep getting

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interrupted by the help desk to create new user accounts.

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You decide that your only hope for getting a couple of hours uninterrupted.

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That would give you some time to work on these projects and meet your deadlines is to actually automate

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and offload this account creation process to some other group.

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So you decide to go ahead and create a shell script.

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Test it on your local system and then upload that shellscript to where it can be used by staff of the

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helpdesk for example and that way they don't have to call you an email and interrupt you and you can

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focus on more high level work.

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So once you've decided that you're going to write this script you sit down and think about what should

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be in the script what it's got to do how it should work.

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If there are any checks you need to perform and so on and so you just scribble down a little list and

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here's what you've come up with.

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You decided to name the skip and local user dot sh.

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You also decide that you want to make sure that whoever is executing the script does so with root or

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super user privileges so that the account creation process can work.

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And if they don't do that if they don't run it as route or run it with sudo for example then you want

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to make sure to quit the script and exit out and you also want to follow standard command conventions

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and shellscript conventions by exiting with a non zero exit status.

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If the script doesn't fully complete properly so then you think about the next scenario where they actually

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do execute the script with the proper privileges.

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What information do you need from the person that is running the script in order to create an account.

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And of course you need at least a user name.

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You'll also want the full name of the person that will be using the account or who they helpdesk is

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creating the account for.

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And then you'll probably want to request an initial password so you can set that on the account.

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So the next thing that the script will do obviously is to take all that information and to create a

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local Linux account.

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From your experience as a Linux system administrator you know that from time to time the command that

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will add a user to a system will fail for various reasons.

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One reason might be that the person executing the command would supply a user name that is already in

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use and then they user add command will fail.

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So you want to account for those situations and you don't want to tell whoever's running the script

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that a user was created when in fact the user was not created.

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So you want to make sure that the user add command in your script executes properly.

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And if for some reason it doesn't you want to stop the execution of your script and just tell the person

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running the script that the account was not able to be created.

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Now at that time they will probably escalated to you or your team and you have to go in and figure out

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why it didn't execute properly and you don't expect the helpdesk staff to do that.

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But you want to make sure to not tell them that a user was created when in fact it wasn't.

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If on the other hand the user was created successfully you want to display the user name the password

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and the host where the account was created on.

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This way the person that's creating the account or running the script can take that information and

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deliver it to the end user who actually use the account that was created.

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So the user will know what their username is what their password is and on what system that that account

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exists on.

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By the way and the lessons leading up to this exercise we didn't explicitly cover how to determine the

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hostname of the machine that you're on.

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I've left that up to you so you can get used to referring to the bash man page and looking for the information

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that you need.

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Getting help and so on.

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You'll use the exact same concepts that we've used explicitly in the previous lessons for example how

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to look up a user ID and so forth.

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But I didn't give you the exact answer because again I wanted you to get that practice so you can do

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it on your own and this way if you ever encounter something that you're not 100 percent sure about you

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have the practice of going about how to find that information.

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So at this point you know that you're going to create a script you know what the scripts are going to

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do how it's going to work.

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And so now what you want to do is test it on your local machine before you turn it over and let other

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people use it.

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So the first thing you want to do is start a command prompt or terminal on your local machine.

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Then we're going to move into the class folder from here we're going to initialize a vagrant project

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called local users.

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If you've been following along in the earlier lessons you'll already have this folder.

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You don't have to do the make command but if that directory doesn't exist go ahead and create it.

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Now move into that folder and initialize your vagrant project.

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We want to give some indication of what machine we're logged into.

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So let's go ahead and set a hostname for this machine and we can do that by editing the vagrant file.

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Do that with the config that VM host hostname equals.

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And I'm going to set this to local users and then right and quit see my changes here.

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Now we're ready to bring up the VM and connect to it.

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So we're run vagrant up to start the VM

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OK.

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Now that the virtual machine is up let's connect to it with vagrant S-sh.

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So now let's move into the shared a vagrant folder which is mounted inside the virtual machine at slash

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vagrant.

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So here you have a choice either to develop and write your script inside the virtual machine or to develop

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and write your script on your local machine but save it into the shared folder.

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Again I'm a big fan of them so I'm just going to create the script right inside the virtual machine.

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We already know that you decided to name it add dash local Desch user not S.H..

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So we'll go ahead and use that filename.

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I'm sure you know by now that every single script we're going to write starts with the shebang.

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And then now we're going to put a header at this file to give anyone who looks at it an idea of what

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it does.

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So this group creates a user on the local system and we're going to tell them what we're going to ask

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them for.

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We're going to ask them for the username.

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It's also called the log in the person's name that would be used in the account and a password for that

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account.

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And finally the main thing that this script does is display that information.

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If you think back to the shellscript requirements that we came up with we wanted to make sure that the

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script was being executed with super user privileges.

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So let's check for that.

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First off there's no need to prompt them for a user name or password.

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If we're not going to be able to use it anyway so let's just do that right at the top of the script.

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We'll use an if statement

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we're going to check the you ID that is set by Bassets a shell variable that gets set anytime bashers

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started.

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And this variable you idea is read only so it can be changed so we can trust it.

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Another thing we know is that the root account always has a id of 0.

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So we can test against the idea of zero.

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So if the ID is not equal to zero which means they're not executing with super user privileges then

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what we want to do is give them a message.

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So we'll use this chance to teach them how to use the script and then we want to follow convention and

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exit with a non zero exit status.

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Since we're not doing anything specific with these exit statuses we'll just use one.

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Finish up our IF statement here and that is our check for super user privileges.

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Now if they have executed the script with the proper privileges now we need to start collecting some

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information and we know how to do that by using the read shell built in.

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So let's build that right now.

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We'll give them a prompt which dash P stands for prompt and we'll follow that with enter the user name

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to create.

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We're going to use a space so that when they start typing it's not mushed up against the colon there.

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We're going to assign what they type into a variable and we're going to call this variable user underscore

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name.

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Now by the way when you're writing this script you could have chosen any other name for your variable.

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You might have said log in here you might have said account name you might have named it dog or cat

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which doesn't make any sense but it's valid syntax so in theory that's OK.

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So before I go any further I do want to point out here that this is one way to implement this shellscript

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and there are multiple ways and that's one of the things that I love about Linux and shell scripting

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specifically is that there are multiple ways to do things and it allows for some creativity and individuality

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while still being able to do useful work and allowing other people to read your code.

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So just know if you use a different prompted if a variable name that is totally acceptable.

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The main thing is does your shellscript deliver on their requirements.

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For example this group does it exit when it's not executed with super user privileges.

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If it does then you did it right.

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And if it doesn't then you need to adjust your code.

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Ok enough aside.

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Let's keep going on here.

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So now we have the user name the next bit of information that we want to collect from the person running

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the script is their real name.

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And actually this is just going to be the contents for the description field or comment filled in the

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password file.

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So this may or may not actually be a real name for example if someone is creating an account for an

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application this might be the application name.

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So we're going to go ahead and account for that in our script because we're thinking of it now.

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Now if you just said real name or person name that's totally fine as well.

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We're going to call this comment.

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And now the last bit of information we need to get is the password.

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Again we'll use the read belt with a dash P to prompt the user.

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And we're going to assign this to the pass word variable.

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Now that we have all the information we need we can go ahead and create the account

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hey we'll use the user add command and the user add command requires root privileges.

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That's why we did the check at the beginning of the script.

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So what we want to do here is use the dash see option and supply the comment or the name or whatever

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that was given to us.

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And that is stored in that comment variable and we enclose that in quotes so that even if there will

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be spaces in this comment it's all treated as the comment.

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So Jane space Smith will all go into the comment field and it will not be interpreted as two different

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things Jane being one thing and Smith being another.

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Now we want to ensure the home directory gets created so we can use the dash him flag.

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And then finally we need to specify the account name the log in name or the user name as I like to call

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it.

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At the end of the user at command here so we talked about this earlier we want to make sure that this

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command succeeds and how we can do that is to check the exit status of the user and command.

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So let's write a brief comment about it and then implement that check.

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We don't want to tell the user that an account was created when it was a

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hey we'll start off our IF statement double brackets will make sure to use a space and then we know

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that the exit status of the most previously executed command is stored and dollar sign.

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Question mark.

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And so again as convention holds if it's an exit status of 0 That means everything.

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Well the command succeeded.

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And if it's not zero then something went wrong.

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So if the exit status is not equal to zero that's what the dash and he stands for.

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Then we're going to display an error message

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and then we're going to exit our script with a non-zero exit status.

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Now assuming that we get past the if statement in the script that means the user had command succeeded.

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Now what we want to do is set the password for the account

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we're going to echo the password.

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And then we're going to pipe that output as the input to the password command.

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SS W.D. with a dash dash s t d i n option.

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And we're going to supply the username if we want to be really safe.

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We can also check to see if the password command succeeded.

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And if the password was properly set on the account again if something goes wrong here then the account

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is not fully completed so will want to exit with a non-zero exit status.

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So again we'll check for dollar question mark.

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If it doesn't equal 0 then display an error message.

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And then exit with an exit status of 1 and finish our IF statement.

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Finally what we want to do is force the password change on first log in

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and we can do that with a password command with a dash option and give it the user name that we're operating

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against.

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So at this point you could even do another check to make sure that this execution of the password command

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succeeded.

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While I'm looking at my script here I notice that I did something that will probably work but is not

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a best practice back in my previous IF statement here.

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I forgot to enclose this variable in quotes and I want to make sure I do that.

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So let me go ahead and add that back in.

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So now we set our password.

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We force the password to be changed on first log in.

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And so now what we want to do is display this information to the person running the script so that they

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can then handed off to the user that will be using the account so we're going to give them the username

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and password and the host where the user was created.

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Now I know the password command generate some output and I want to separate this output from that output

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so I'm going to use the echo statement on its own without any options or without any arguments.

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The echo statement displays what is passed to it and a new line.

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So if you don't pass anything to echo it's ultimately going to print a blank line.

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And so that's what we'll use it for here.

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Now let's display the user name and will display this on the next line.

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Let's add a blank line and we'll tell them the password.

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And finally we want to tell them the host.

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So at this point if you don't know how to get the hostname what you can do is look at the bash man page

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and let's do that really quickly now see my changes type man bash.

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So let's perform a search and see if we can find anything about a host name and the bash man page and

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perform a search we'll use a forward slash which is a Ford search will type hostname and press enter

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and sure enough we come to something that is in all uppercase letters.

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And as we know by convention something in all uppercase letters can be a variable name.

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So this variable says that it's automatically set to the name of the current host.

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So if we scroll back up here we can make sure that this is indeed in the variable section and will keep

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going up here.

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And sure enough it's in the shell variables.

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So we can get queue to exit out of here.

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Let's look at the value of it.

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Get it set to local users which is the name of our system that we're currently on you can see our username

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vagrant at local users.

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So let's get back into our shellscript and and that last bit of information.

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So if we get to this point the script is really complete and it's completed successfully.

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So by convention we need to exit with a zero exit status so we can do that with this.

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Now let's save our script and start testing it the first time we execute this script.

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We want to make sure that it has executable permissions

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OK.

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Let's go ahead and add a user with a script that we created.

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Let's create a username of Einstein the real name will be Albert ein stion and the password will set

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to something like E equals MC squared theory and end it with a dollar sign.

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Hey we get some output from the password command and then we get the output that we displayed at the

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bottom here the user name the password and the host that it was created on.

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So it looks like the script function normally we can check the exit status with Echo dollar question

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mark.

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Sure enough we have a zero exit status so that all looks good.

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Now let's look at the ETSI password file to see if the user was created and used the cat ETSI password

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command or even the tail ETSI password command which will just print the bottom of the file so you can

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see it the last line of the file here is the Einstein user and that the comment is included in the account

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line and everything looks good there.

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To really test if the account was created properly let's go ahead and switch to that user.

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So I use su for switch user space and dash to get the users log in environment space.

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Einstein which is use name.

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Now it's prompting us for the password which we can enter now.

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Sure enough it accepted the password that we supplied when we executed our script and now it looks like

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it's forcing us to change the password which is exactly what we wanted to happen.

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So let's go ahead and retype in the current password.

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Now let's go ahead and give it a new password something like let's say crazy hair and end it with an

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exclamation point.

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OK.

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Now that we've proven that the script works for creating accounts.

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Let's see what happens when we execute the script without the proper privileges.

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So I'll just type and exit to get back to our vigor and account.

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So let's do this dot forward slash add local user dot SH sure enough it exits the script doesn't ask

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us for the account name or the password or any that doesn't attempt to create the account which is exactly

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what we want to happen.

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It gives us a status message here that teaches the user how to actually use the script which is really

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good.

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Now we want to check the exit status and see it here.

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Ecko dollar sign questionmark and press enter.

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Sure enough it's a non zero exit status.

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So our script fits all of our requirements and it works exactly as expected.

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Again I just want to say that if you didn't come up with the exact script that I did line by line that

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is ok as long as these tests pass because that means that your script works and that's all that really

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matters.

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Ok I hope you enjoyed writing this script.

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Now we're going to move on and learn some more about shell scripting.