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Unit 02 - Using Linux

13. Topic B: Command Line Linux

Alright, so now we're going to talk about the command line option. So, you saw some examples of the graphical user interface. It looks so much like the Windows command line that it's going to feel and look a lot different than the command line you get in a Windows environment. So we're going to talk about the CLI command-line interface and what we often call the shell.

14. Command Line Interface

All right. Some people tell you that you can perform nearly any Linux task at the command-line interface. I'd like to go a step further and say you can do almost every task or every task. I'm not sure why we're afraid to commit to 100%, but we can do almost everything you want through the command line. It is called opening a shell. A shell is nothing more than your interaction with the kernel through a command-line interface. There are a variety of different shells. I'll tell you about the Bash shell, which is the most common, the TC shell, the Zshell, Public Domain, and Corn. All of these are different types of shells that you can use that allow you to enter commands, retrieve data, and interrogate people. Remember, it's not just about sending configurations or sending commands, but it's also about retrieving information to see how the system is running as well. And in working with a shell, it can be in an interactive or a non-interactive mode. So we'll talk about each of these here as we continue on through this section. But again, it's just to make sure you understand that this is not a pretty GUI, that it is a series of commands that you can type in, hit Enter, execute, and either see the results of it or make changes to your configuration, whatever it is that you want to do. Remember that a shell interacts directly with the kernel; it does not use an Xwindows, which is a fancy GUI that looks like a command-line interface, as you might find in Windows. This is directly connected to the operating system, and you can do, as we've said, nearly anything you want.

15. BASH (Bourne Shell)

So the bash shell, also known as the Bourne shell or, more accurately, the "born again" shell, is probably one of the most popular now. Originally, the Bourne shell came out in the 70s. It was retooled and reintroduced, which is how they got the kind of pun in there of calling it "born again" because the person who gave it that name was born. It was designed as a command-line environment, and it was not necessarily GPL licensed. That presents a problem. If it's not open source, anybody can use it. Then you have to use many tools that work and behave like the bash shell. But doesn't the bash shell give you that same functionality? So really, you have to be careful. When we talk about a Bash shell, is it something that is licenced to you or is it something like it? Anyway, whatever the case is, we're going to talk about how to use these shells and what they do for us. Now, there are many tools and commands that you can use to make this shell very easy for you. and we're going to talk about some of those tools. They're all keyboard commands or keyboard shortcuts, using arrow keys and some other type of function. And by making it easy for you, what we're saying is that it reduces the amount of typing and all the work that you have to go through to be able to issue these different commands.

16. Common Commands

So some of the common commands that you're going to see and hear in demonstrations would be commands like "cat," "clear, date, echo, exit, finger.LS who? Who am I? And you might say, okay, great. What do they do for us? Well, again, it just depends on the command. Clearing the screen will clear the screen.The date tells you the date. Echo will repeat information; exit will shut things down. Finger figures out who somebody is. LS will list the files. Who am I? telling you what user you're logged in as. I mean, we can just keep on doing that, but to just sit there and read and rattle off a bunch of commands without actually showing you how they work is sometimes difficult. So that's our biggest goal. We're going to show you these commands in demonstrations, but it's just important that you understand that there is a list of commands that you're probably going to use over and over and over again. So you're going to get used to those. And so we're showing you some examples of those common commands.

17. Demo - Entering Commands at the BASH Prompt

Alright, so we're going to take a look at yet another option here with, in this case, the KDE desktop environment. We're going to play with the Bash shell. Now, you probably see a lot of times when I'm going back and forth between the different operating systems. I do believe it's important that you get familiar with them all, at least the two big ones. But you're going to see that a lot of these are the same commands. So what I did was take this little shortcut to get to the shell here. So that's what I did. To open this up, I'll kind of move it down here towards the middle of my screen. And what I'm going to do is simply start showing you some commands. Now you already saw this one, "Who am I?" And it tells me that I am logged into the route, and that works out okay for me. But now let's take a look at some other options. When I did PWD, it told me which directory I was in. I was on the slash route. We'll talk about some commands like ls to show you what's in that slash root, which isn't a whole lot of anything, but I don't have to change directories to get to do the ls. I could provide a path like "show me what's in the user directory," and it would show me all the information in the directory called the user. So I think you can get around pretty straightforwardly with some of your commands just by knowing the paths. That is simply a list of all files. And remember that all things are considered files in the world of Linux. Well, let's try LSP with some of our options. In fact, let's try the double dash Help. And wow, watch out, we just got hit with a whole bunch of stuff. Remember, Help was designed to be able to provide information about that particular command. And wow, take a look at this. This help is showing you all of these arguments that I could use to help me provide more information about the way this command works. Now I'm going to try this lowercase L, not an uppercase L, in just a second to see how that changes the listing format. When I just did so, let me scroll back up. When I just did the LS with no options, it just showed me the names of all the files and/or directories simply by leaving them in their names. It alphabetized them, going left to right, top to bottom. So this Dashl says it'll use a long listing format. And there are a lot of these great things that we can do. We can change the types, and the list goes on and on. I would really tell you that you want to play around with this so you can see how you can use it and learn what things it does for us. So let's try the LSL for that same user directory, and let's see how that changes the information. Well, what it did for me now is that you can take a look and see if it has added more information. Now, later on, we're going to be talking about what all this Rwx Rwxrwx stuff is. But in short, those are permissions read, write, and execute, and it tells me what type of files these are, but we're going to define those for you a little later on. So I'm going to leave them for you to just kind of drool over and wonder what they are. From there, of course, we can see information about the owner. We can see which is the primary group and the size of the file when it was created. A lot of information is available to us in the filesystems, but like I said, that's another unit coming up. All right, so what else can I do? Well, hey, look, if it's too busy of a screen, you can type clear and clear everything out of your way. You can type simple little commands like "date." It shows you the current date. If I type in "cal," it shows me the calendar and kind of highlights the day that I'm on, and again, it clears all those things off. So it lets me kind of play around with things. Now remember that your commands are case-sensitive, and if you don't type them right, you're going to get some problems. Like, if I tried, then who am I? command and I typed in "Whao." I don't know, is that like riding a horse? I hit enter, and it says, Hey, that's not a command. Well, that's something I kind of expect to see because I didn't type things incorrectly. So sometimes you have to get a little bit of help or look maybe in the past and say, "Well, what was that command?" Well, the nice thing is that I can use the up arrow, which is what I'm doing right now. And the up arrow is going to take me through a list of all of the commands that I have typed in the past while on this particular terminal or shell; it will not show me commands in other shells as they are considered to be exclusive of each other. If I see those commands and I can say, "Oh, yeah, that's the command I wanted," well, I don't have to retype it now. All I have to do is hit Enter, and it reruns the command. And in fact, if you wanted to see all the commands that you've run in this particular shell, at least, I believe, probably up to the last 500, you type in history, and it shows you a history of all the commands that you've gone through. It's kind of a nice way for you to be able to keep track of what's going on. And, once again, if you've mistyped one and can't remember what command you just executed, Well, there are some options that you have, okay? Other things you can do are: if I type in "who" and I just don't remember what the rest of it was, I could try to use the word or the tab key. And what the tab key does is show a list of the commands that begin with the letters "who." kind of like a little bit of help. Now, if I type WHA, that's the only command that actually starts with those four letters. So now if I hit the tab key, it finishes it for me. So that's also a nice way to be able to get around and fill in the commands, especially when you're new to this and don't know what they are. I mean, look at this. I can type W into a tab, and it shows me all of the things that start with W. I mean, it's kind of crazy, isn't it? And in fact, that means hitting the spacebar to see even more on that same page. Okay, so tab completion is something else you can do. Now, if you have a really long command, okay, this is not a command at all, but now you find that you need to navigate around, like, for instance, that word. Now, maybe it actually should have said no, and I need a K in front of it. You could park your finger on the arrow key going to the left and get all the way down there. or control on the letter A was designed as a shortcut to take you to the beginning of the line. Now, this is considered one of the standard types of options that you have. Control A, like the beginning of the alphabet, takes you to the front. Control E, like the end of a line, takes you to the end. Control-B lets me go back a word. Control F. Let me I'm not sorry a word, but a whole character. Control F lets me move. You have some other things you can do to just blow things out. Let me control B. I can do Control-D to delete a letter, but I can't replace the letter with a control command. I'd have to just retype it. The other option you have is to control W. erases the word on your left. You kind of get the idea, if I didControl U, it erases everything on my left anyway. So you get some options and begin killing things. and let's see. Control e, control u. There we go. Erase everything that I have. So these were called Emacs, and the reason we had them is because in the old days of terminal emulation, the up arrows didn't register. They didn't work. And think back. There was a day, believe it or not, where we had no errors on our keyboard. All right, well, that was kind of a way of giving you a little bit of a tour of this particular shell. We're going to see some more commands later on to help us through some of the stuff that we want to be able to do. I'll show you some other examples of help, but what's important to see is easy ways to navigate, looking at the history, and being able to kind of work with that. And the next time we come in here, we're going to type a little bit of history again. We're also going to play with some of the environmental variables. Bye.

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