Tuesday, September 2, 2008

The Linux Terminal For Beginners

source:

http://davestechsupport.com/blog/2008/06/14/the-linux-terminal-for-beginners/

A very long time ago, computers didn’t have mice, icons or fancy graphics. Instead of an Operating System with a Graphical User Interface, there was the Command Line Interface. With it, you would issue commands to your computer in a text only environment that is not seen so often these days. But many computer technicians, especially Linux geeks, consider it to be one of the best ways to interact with the PC for certain kinds of tasks. Though there is a little bit of a learning curve about it new users shy away from . So I’m going to try and flatten that curve with an introduction to the Terminal window for beginners.

Understanding the Command Line

To help get a better feel for the Terminal, you should open one up right now and follow along with this guide. To do this (in Ubuntu) click Applications>Accessories>Terminal. Once you do, a new window will appear with a command prompt and a blinking cursor. The prompt typically looks like this:

username@hostname:~$

The username is your username, the hostname is the name of your computer. The tilde symbol “~” is shorthand for “your home folder”. And the dollar sign indicates that you are currently operating under a kind of limited privilege mode (if you were running terminal with Root level privileges, the $ would be a #. More on that later). Following all of these things is a blinking cursor, which is your cue to begin typing a command into the Terminal window.

In the above screenshot, we have our Nautilus file manager to the left as well as a small terminal window on top of it where I’ve typed in the commands “cd Documents”, followed by an “ls” command, pressing Enter after each. If you’ll notice, the “dear ubuntu forum moderators.odt” file is shown in both the terminal window as well as the file browser. It’s the exact same file, and I used those two commands in Terminal to “browse” to the folder containing that file and list the contents of the folder. So we have two commands here that we can talk about briefly:

cd - Change Directory (e.g., “cd Documents”)
ls - List current folder contents.

When you first start Terminal, you are usually placed in your Home Folder (which is indicated by the ~ (tilde) symbol). If you type ls and press enter, you’ll see all of the files and folder contained in your Home Folder. Try to practice navigating from your home folder to some other folder using the cd command. NOTE: All Linux commands are Case-Sensitive! Once you’ve navigated into a folder, or perhaps into a folder within another folder, you can go “backwards” to the parent directory by typing “cd ..

Exercise 1: cd and ls

  1. Click Applications>Accessories>Terminal
  2. Type ls to view the contents of your Home Folder
  3. Type cd Documents and press Enter to navigate into the Documents folder.
  4. Type ls to see the files (if you have any) listed. Then type cd .. and press enter to return to your home folder.

Ok, how about a few more commands?

As shown above, the cat command can be used to create new files, but it can also be used to append text from one or more files to the end of another file… but we’re not going to get that advanced. We just want to create a new file and play with it using other terminal commands.

cat - Create new files, combine text files and display them
cp - Copy
rm - Delete/Remove

Using these commands, we’re going to create a text file, copy it, then delete the first copy.

Exercise 2: cat, cp and rm

  1. Open terminal, and browse to the Documents folder by typing cd Documents, and press Enter
  2. Create a new text file by typing cat > foo.txt and press Enter.
  3. You’ll be sent to a blank line just below the command prompt. You can type whatever you want, starting a new line each time you hit Enter. It’s a basic text editor. When you’re finished typing, you can save and exit by pressing CTRL-D.
  4. Type ls to see the new file in the directory. To display it’s contents, you can type cat foo.txt.
  5. Copy the file by typing cp foo.txt foo2.txt. Type ls again to see the new second file.
  6. Delete the first file by typing rm foo.txt, and then type ls again to see the change you made.

There are other commands out there besides cat (such as touch) that can be used to create new files, but we’re trying to keep this short and simple.

Now lets create a file, then a new folder, and move the file into that folder. We’ll do this with the mkdir, mv and ./ commands. The ./ command in particular is interesting — it basically stands for “the current directory you are in”. Sound redundant, right? Here’s why you need to use it: There are many commands in the Linux system that can be run from any directory, such as the ones we’ve been using (cat is an example). These commands reside in a location of the computer that’s been designated to be available at the terminal no matter what folder you reside in.

So say you created a computer program called “cat”, but had nothing to do with text files, and more to do with the feline animal. If you simply typed “cat”, Linux would assume you meant the cat program we used to create a text file, and not yours. By adding the ./ in front, it forces Linux to focus on that local folder you happen to be in.

Exercise 3: mkdir, mv and the ./ delimiter

  1. Open terminal, and cd into you Documents folder.
  2. Type cat > foo2.txt, press enter, type some text, then CTRL-D to save and exit cat.
  3. Type mkdir foocopyfolder to create a new folder. You can type ls after this to see it.
  4. Type mv foo2.txt ./foocopyfolder/ to move the file into foocopyfolder
  5. Type ls to see that the file is now missing, then cd foocopyfolder, and then ls one more time to see the recently moved file.

Other Useful Commands

By now, you should already be familiar with the basics of the terminal. Here are some other commands you can experiment with:

rmdir - Remove Directory
sudo - This is typically inserted in front of any regular command that requires root level privileges in order to do. You can think “Super User Do” to help you remember how it’s spelled and what it does. For example, if you wanted to execute a command that required root privilages (such as installing a program) you would type “sudo apt-get install vlc”. Remember, the terminal windows is Case-Sensitive.
locate - a useful index-based file search utility
lspci - Lists PCI devices in your computer (used for technical troubleshooting)
lsusb - Similar to lspci, but for USB devices
apt-get - This is used very often to install, remove and update software. An example of this command would look like: sudo apt-get install vncviewer. Note the sudo in front.

The Manual Command

Now, a lot more could be said about these commands. If you ever want to read all you can read about any one command, you can do that with the man command (which is short for Manual), followed by the command you’re interested in reading about. For example, if I wanted to read about all the different options for the ls command, I would type man ls. When viewing a manual for a command in terminal, you can use the up and down arrows to scroll, and then when you’re done reading, you need to press the Colon key : followed by the q key. This will take you back to the Terminal window.

That’s all I am going to write about the Terminal for today. The three very simple exercises above should have you feeling just a little more comfortable with the Terminal and navigating around your file system. Here are a couple tips though, in case you get lost:

cd / - takes you to your root directory
cd ~/ - takes you to your Home Folder.

And just so you know, your Home Folder is actually located in /home/yourusername/.

There are a lot of great guides out there that go into a lot more detail that I’m willing to do here, so check Google to see what you can find. Here’s one that I think is pretty clear and concise that you should take a look at if you intend to learn more about the command line.

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