Unit 02 - Using Linux

23. Demo - Exploring the BASH Command Line Interface

Alright, we're going to revisit this console as I promised. We're going to take a look at some other commands. Remember, the goal here is just to start getting you comfortable and just to remind you, right, the first command we did was who am I? Remember, there was a history command. If I can spell history, that shows you a list of all the commands that you've typed in the past. So here's a list of my commands. And the last command, obviously,that I typed was history. And if I wanted to repeat that command, we told you to use the up arrow, hit Enter, and type in that command. Notice how my last two commands in our history? So it didn't just say, "Oh, you repeated it." Now if you hit the double exclamation point and type in Enter, it actually reruns the same as the up arrow and the Enter key. So it lets you go and do that again. You could also use the up, exclamation, and number keys. So there is a number 33, that should go with the whoam I command, and it runs that command for you as well. So, I don't know, it just gives you some ideas of things you can do and a few tips and tricks about using the shell. Alright, let's focus on the LS command. Remember, LS was designed to show you the contents of a directory. In this case, it shows the contents of the current directory. If you don't know which direction you're going in,PWD showed you where you are at. In this case, we're at the root. We can also type in LS, adirectory, putting in the actual path. So even though the user directory is not a subdirectory of where we are, it would show us what is in that particular directory because we named it by its absolute path. And we saw some of the other options that we had with LS and doing those little things like LSLand putting that same information in as well. Okay, there are also a number of different variables that you might want to work with. Remember that there are lots of environmental variables. One of them, we said, was the random number generator. If you want to see the value of a variable, the echo command was designed to toss that content out on your screen. One of the variables was this random number generator. So if I say echo random, it basically just creates a random number and shows that to me. In fact, if I do the double exclamation point, there it is. It ran that same one again and gave me a different value. All right, some other things happen when you type in commands. Sometimes you type in commands that just don't work. As you may be aware, this LS user worked with devices. Watch out. This thing is a huge directory. There are lots of different device options that are out there. LS home. Nothing really in the home directory. But if you start putting in directories or paths that don't exist, like home bogus, then you are going to start getting some of the error messages from the operating system talking about whether some things actually exist. Now, if I said let's change our directory to homebogus, well,I expect them to say no, you can't do it. But we also said, "Hey, you can add in some extra commands." So let's try this again. Let's do CD, home bogus, and let's do the double ampersand and then type in LS. That means we want to list things. Well, again, no such file directory,so it wouldn't let me. But if I wanted to change to the userdirectory ampersand ampersand LS, it does that for me because, remember, that was doing an and A logicaland both things had to occur. I had to be able to basically be able to switch to the user directory and to be able to list it. And because both of those worked, that happened for us. Okay, so I'm going to back up to where I was before CD. Actually, I was in the roots, if I remember right. So I'm going to go back to the directory, type in PWD, and I'm back there again. I've got too much stuff on my screen. I'm going to clear it off. Imagine what my history looks like now. Well, let's try that same CD with the home and bogus track we know doesn't exist. But I don't use a double pipe commando type LS, so what happened here? It did the LS command form right there where it says desktop. But the reason that worked is because the double pipesmean or switch to the home directory or run LS. Well, or means, if one of them is true, then do it. In this case it did the desktop command. So, once again, I'm just reminding you of some of the really cool things you can do in terms of moving around, doubling up your commands, and having fun. Okay? So CDB, remember, if you don't know the end of a word, the tab, which is what you just hit, helps you complete that particular option. So I'm going to say CD bin because the tabkey showed me that that was one of my directories. I'm going to list what's in my binaries. And look at that. There is just a tonne of stuff in my binaries. In fact, I can't even see it all. I'm going to have to scroll up just to be able to see the rest of the stuff that's here. In this case, one of the other things that we'll see Let me get my mouse back to normal again. I've decided to try to jump outside of my setup here. Okay, so let's scroll up here and you can see that there is a very large amount of information. And so one of the problems we have is, hey, I don't necessarily want to have to scroll. I want to look at things as I'm going through, and so what can I do? Well. Again, Remember, that's where you go to your help commands and see if there were any options, but I'm going to try this LS with the word pipemore, which means take the output basically. The LS command takes the output from the LS command and shoves it into the more command, and what you see here now is that I have to hit the space bar to be able to look at all those options in the LS if I hit the letter Q. It quits it out for me so I can get out again. It's just good to know all of the options that are available to you as a method of making life a lot easier as you're doing these different commands alright. So I'm going to move back to my root directory, which is technically this funny little squiggly line I believe it was a tilde, which returns me to my rootdirectory, or I could have typed in CD root and clearmy screen, which takes me out of the whole process of dealing with different types of commands. So what you're seeing there again is more ways of navigating around the command line and I realise you're spending a lot of time talking about that, but this is probably the one area that most of you are unfamiliar with, so I want you to kind of get comfortable and practise and play and use the help and figure out how to get around your command shell. It's a very important tool that will help you in Linux.

24. Piping

Now, one of the things about these commands is that the output that you get might be something you need to feed as input into another command. We call that piping. Now, piping has some other capabilities for us as well, such as filtering large amounts of output. But basically, filtering is another command, and we're feeding the bulk information that we asked for into the filter command so that it filters what we see. Another example is piping. So the output of one command is input into the next one, and it uses that up and down vertical character that we call the pipe character. Again, like I said, it could look like two little dashes that are both vertical right above each other.

25. Piping and Redirecting

We can also redirect our command to be able to control its output or input if we want to through the use of a greater than or less than sign. So I can actually take the results of a command and output them, redirect them to maybe a text file or maybe something coming in from a certain device input, like from my keyboard, that I want to have redirected into a particular command or file location. So I can do that as well. I can manage things through redirection again using the command line. You can imagine that you could probably use all of this, right? You can have a large output piped to a filter, redirected to a file for output, or you can put them all together and then have that with the double ampersand. And something else, that's what I'm trying to say, is that you have a lot of creativity available to you, as creative as you want to be. And how you issue these commands with all of these meta characters, all the piping, the redirecting, your environmental variables, your self-made variables, all of these things can really give you a robust environment to do almost anything you want to. In Linux.

26. Standard I/O

Now, one of the things we generally deal with when looking at these variables in the shell is the idea of the standard in standardout and standard error. These are just kind of given things that we have configured. The STD in standard input is generally our way of representing the stuff that comes from the keyboard. Standard output is generally the stuff that's going out to the monitor. We used to say it was the stuff that went to the printer, but more likely today it's the monitor. The STD AIRR standard error is frequently a result of an automatic redirection to the standard output device. Again, if an error occurs, bam. right onto your monitor. Those are other things that we can use to help in redirection as well.

27. Demo - Exploring Piping and Redirection

Alright, we're going to take a look at some more of these little commands. As I've promised, I'm not going to do the who am I anymore. And just as a reminder, we're going to do thisLS command and we're going to look at the devices and see how big it was.And we started talking about redirecting and piping. And the piping was just a reminder that when you do a command like the LS dev, the output of that command will be sent through whatever pipe you create to another command. In this case, I'm going to pipe the output of the listing of the device directory to the more command. And you remember what that did? It overrode that default behaviour of shoving everything onto my screen and gave me the opportunity to hit the spacebar and look at all of these things one at a time. All right, letter Q, let me quit, let me clear the screen, and everything is all set to go. Now the next thing I'm going to do is I'm going to hit the LS command. You see, I have only one thing here, and that's the desktop. And I'm actually going to go out and make a directory, make a directory in the home folder. I'm going to make the one called Ken and then I'm going to move to that directory and list the contents. And there's nothing in this location. One of the commands we talked about was this thing called T. And T was a way of creating a file. I'm going to call it Getnasaenfo. And the way T works is that as I hit Enter, it allows me then to start typing here and putting whatever I want in here. And I'm going to actually create what's going to kind of look like a little script of commands like open, ADC, GSFC, NASA, gov. Now when I hit Enter, it's going to echo what I've typed. That particular site might want us to log in,so I'm going to log in as anonymous. Then I'm going to ask it to change to the pubadcfolder. Then we'll tell you to get the contact underscoreinfoTXT folder or file and exit. Now exit is just something I'm typing into this actual text file. It's a text message. To actually exit out of here, I need to hit control. C Controlc is almost universally the way you stop the execution of almost any programme on almost every operating system. So that's something you're going to want to remember. I'm going to list the contents of my folder, and I've got the getnasa info. I'm going to use the cat command so that I can print the contents of that folder. And look at this. I'm going to hit the tab key. Boom. Hit the tab key out there so I can show you the contents of that file. And even though you saw it double up, because of the way in which it was echoing everything I typed in that file, it still showed you the contents of that particular file. Now, if I wanted to, I could use the redirect. I could redirect this kind of information like the FTP command. I could redirect the contents of the NASA info to FTP. But in this particular case, I don't have an FTP server set up. And we'll look at some of those options a little bit later on. But you have to remember that the redirection was just that; it was sending the data of one thing to something else. And it's kind of a nice way of being able to move data from one file to the next, however you want to take care of moving stuff around. All right, that was kind of a quick little tour, again, showing you some more of these commandline options and using commands like t and LS and make directory. And I'm going to keep encouraging you to create your own, so not create them, but to practise with them and get very comfortable with moving around the operating system, moving around the file structure, and the things you can do.

ExamSnap's CompTIA XK0-004 Practice Test Questions and Exam Dumps, study guide, and video training course are complicated in premium bundle. The Exam Updated are monitored by Industry Leading IT Trainers with over 15 years of experience, CompTIA XK0-004 Exam Dumps and Practice Test Questions cover all the Exam Objectives to make sure you pass your exam easily.