< ~wiki

Command Line Shell, for Absolute Beginners

So, you want to join a public-access shell community like tilde.team, but you don't yet have experience using GNU+Linux or other UNIX-like operating systems? This tutorial is designed to give you enough guidance that you can get started and move on to successfully directing your future learning. Once you get a basic level of self-sufficiency, tilde.team is a great place to practice and learn more.

GNU+Linux is a text-based operating system. And it takes work and thought to start using.

You'll find a lot of people online arguing that GNU+Linux is not a text-based operating system, and that it in fact has a GUI interface just like Windows. It is true that you can use GNU+Linux through a graphical user interface (GUI) like Gnome, or that you can use services from GNU+Linux servers like tilde.team through a web interface. But the people who are so keen on GUIs are saying this to make GNU+Linux sound like an easy transition for Windows or Mac users. However: (1) to really leverage the power of GNU+Linux, you need to learn to interact with it as a text-based system, and (2) while it is different, it's not really that hard. It will take effort to learn the differences, but that effort will pay huge dividends.

How do I connect to a shell server?

The most common way to connect remote GNU+Linux system is with an SSH client. SSH stands for secure-shell. SSH allows you to make a private connection between your computer and a shell server like tilde.team, and it ensures that nobody else along the wire can listen in on your connection. Check out our SSH page for information on connecting to tilde.team over SSH.

If you are having trouble with making your first SSH connection to tilde.team, or anything else while you're learning from this tutorial, drop by the tilde.team web chat or email an admin for help (sudoers@tilde.team).

What is a shell?

An operating system (OS) is the nuts and bolts that makes all the parts of your computer work together for you. At its core, the OS is not friendly for day to day computer usage. A shell is a user friendly "wrapper" around the operating system that allows you to use it easily. A shell can be graphical, like the Windows or Android GUIs. Or a shell can be text-based. A text based shell, also called a command line interface (or CLI), is a tool you can use to control the operating system by sending it text commands.

What kind of things can you make the OS do? Things like opening files, listing the files in a directory, displaying the current system load, or telling you what other users are currently doing.

What is a command?

Commands are simple words, often abbreviated, that make the system do things when typed into the shell. Some simple examples are 'ls' which lists the files in a directory, or 'cd' which changes your location to a new directory (cd = change directory), or 'exit' which logs you out of your current shell session. There are thousands of useful commands, but you only need to know a few to get started and be self-sustaining.

This tutorial will teach you the few commands that should allow you to take care of yourself and start down the real, longer-term path of self-directed learning. Once you're logged into tilde.team (or any GNU+Linux shell server), you can practice the following commands as you learn them.

What are the first commands a new user should learn?

When you're first starting to use a shell in a UNIX-like environment, you will want to be able to do the following things:

  1. logging in and logging out
  2. list the files or directories in a directory
  3. move between directories
  4. read, write, and save files
  5. create new files or directories
  6. move or copy files between directories
  7. delete files or directories
  8. download files from elsewhere on the internet
  9. learn more about new commands

When you're logged into a shell, you should see a command prompt and a blinking cursor. At this point, simply type a command and hit Enter to run it. You can try this as you work through learning the commands below.

Logging In, with ssh

Recall from the How-Do-I-Connect section above that you can use a SSH client to log into tilde.team. Once you're logged in, you can use the command line SSH client to log into any other shell server; in the example below, let's say you want to log into tilde.town from tilde.team.

Skipping some specifics for now, you can log into tilde.town from a tilde.team shell by using SSH as follows:

ssh tilde.team

Some shell servers allow you to log in with nothing more than a username and password. But increasingly, many servers (like both tilde.team and tilde.town) require you to use ssh keys. To learn more about ssh keys, again, see our SSH page: https://tilde.team/wiki/?page=ssh

Logging Out, with logout or exit

logout is a simple command you can use to log out of a shell. You could also use exit.

Listing Files, with ls

To list the files in a directory, simply type ls. This will print a list of the files in your current directory.

ls

Changing Directories, with cd

You may move from one directory to another with cd. Wherever you are in the file system, you can type cd by itself to return to your home directory:

cd

Change to the directory with your html files as follows:

cd public_html

Read the Contents of a File, with less

If you're still in your public_html directory, you should see a file called 'index.php' when you use the ls command. Let's peek inside 'index.php' as follows:

less index.php

less has opened the 'index.php' file for you to read. You cannot edit it; only read it. Type q (quit) to stop viewing the file contents and return to the shell.

Edit and Save Changes to a File, with nano

nano is one of many text editors availble for GNU+Linux. There are many more powerful editors, but we'll start with this one because it is simple. Let's open your 'index.php' file and make some changes.

nano index.php

Now you're viewing the contents of 'index.php' again, but this time you can change the contents. If you don't know HTML, be careful here. Use your arrow keys to move the cursor down to the line that says the following: <p>Just log in with your secure internet shell to change this file!</p>

Leave the <p> and </p> tags as they are, but change the sentence in between them.

Now, save and quit by hitting the key combination Ctrl+x, and then typing 'y' in response to the question about wanting to save the modified buffer.

Now you can pull up a browser to see the change at your tilde.team URL: 'https://tilde.team/~yourUserName'

Create a New File with nano

Let's create a new file in your public_html directory, called 'testing.html'.

nano testing.html

'testing.html' did not exist before you opened it with nano, so it was created for you.

Now, add some quick contents by opening the file for editing with nano, and adding whatever you want. Then Ctrl+x to save, you will have created a new file.

Type ls to view the contents of your directory an confirm that you did indeed make the file.

Later in this tutorial, we will come back to this file and make it viewable in your web space.

Create a New Directory, with mkdir

First, hop back to your home directory with the cd command (remember that cd from anywhere in the file system will take you back to your home directory).

Now create a new directory called 'downloads' in your home directory:

mkdir downloads

Use ls to see that it was created, and even move into the new directory with cd downloads.

Moving Files Between Directories, with mv or cp

First, cd back to your home directory, and use nano to create two new files called 'fileone.txt' and 'filetwo.txt'.

Lets move those into your 'downloads' directory using two different commands, to demonstrate how they workd differently.

Move 'fileone.txt' into 'downloads':

mv fileone.txt downloads/

Now if you ls the contents of your home directory, you will no longer see 'fileone.txt', because it has been moved into 'downloads'. If you 'ls' the contents of 'downloads' (a shortcut command is ls downloads), you will see it there.

Next, copy 'filetwo.txt' into 'downloads' as follows:

cp filetwo.txt downloads

Now if you ls the contents of your home directory, 'filetwo.txt' will still be there. This is because cp made a copy of 'filetwo.txt' and put the copy in 'downloads'. It did not touch the original file in your home directory. Verify this with ls in your home directory and in 'downloads'.

Delete Files and Directories, with rm and rmdir

As long as you're in one of your own directories (e.g. your home, or 'downloads' or 'public_html'), you can create a new files. Create a new file called 'testtrash.txt':

nano testtrash.txt

Then save it as you have already learned, and confirm that it exists by listing (ls) the contents of the directory.

Now, you can delete the file with the rm (remove) command:

rm testtrash.txt

Notice that you don't get a warning that you're about to delete it, and you don't even get a confirmation that it is deleted. You've learned your first command that you need to be careful with. If you delete an important file with rm, it is gone forever.

You can delete directories the same way, only using the rmdir command (remove directory) instead of rm. If you use mkdir testtrash, you can then delete it as follows:

rmdir testtrash

Note that you can only delete empty directories with rmdir.

If you want to delete directories that still have contents in them, use the following:

rm -rf directoryName

Be very, very careful with this command. Many a user, new and seasoned, has been stung by hastily deleting directories like this. This is also the source of the classic sysadmin joke/horror story about rm -rf / which deletes the entire file system.

Downloading Files, with wget

Now cd into your 'downloads' directory because we're going to use it for actual downloads.

Use the wget (WWW get) command to download a text copy of this tutorial from tilde.team user cmccabe's public_html directory:

wget https://tilde.team/~cmccabe/gnu-linux-toot.txt

You will see output of the command that confirms it is downloading. You can also verify that it has downloaded with your ls command. You can also peek at the contents with the nano or less commands that you learned above.

If you know the URL of other files you'd like to download, you can grab those too, just swapping the URL above for any URL:

wget [URL here]

A brief note on security here, if you do pull any scripts from the Internet using wget, it's important that you do not execute those scripts until you've read over what it does. Otherwise, you run the risk of compromising your account or allowing other malicious actions to take place.

Learn More About Commands, with man (and help)

At this point, you've learned most of the commands you need for basic self-sufficiency in a GNU+Linux shell environment. With just a few more, you can go a long way. When you want to learn more about a command, you can look at its "man page" with the man command. "Man pages" are the instruction manuals for most commands and programs in GNU+Linux.

Try out man by looking at any of the commands you've learned already (except cd*). For example, man ls would open the man page for the ls command. When looking at a man page, type q at any time to quit and return to the shell.

The man command will be one of your most valuable tools for as long as you're using the GNU+Linux shell. You will always be learning new commands and new ways to use old commands, and man will help you do it.

* Note: technically speaking cd is a shell built-in, not a command. Make a mental note of that and you can learn more about the distinction later. For now, note that you can use help cd to learn more about the cd command.

Commands have options and arguments.

When you look at the man page for a command like ls, you'll see in the DESCRIPTION section a number of options that you can use to modify how the command works. They look like -a or -h or -l. Try adding the -a option to ls and note the difference:

ls -a

The -a option now lists "all" contents of your directory, including "hidden" files (aka dot files). You could combine the three options listed above in the form of ls -alh to list "all" files, in "long" form, and display file sizes in "human" readable format. Most commands have

Commands also have arguments, or information passed into a command for some kind of processing. You have already used these arguments when you told nano to open a file: nano testtrash.txt. In this case, "testtrash.txt" was the argument to the nano command. You also used "testtrash.txt" as an argument to the rm command when you did rm testtrash.txt.

Commands will often combine options and arguments, sometimes in specific sequences. You can learn about these when read a command's man page.

The Filesystem Hierarchy

You already know that you get dropped into your "home" directory when you first log in. Your home directory is just one of many, many other directories on the system. All of these directories are organized under one master directory called the "root directory". The root directory is often referred to with a single forward slash, like this: /

You can list all the directories at the root level by using the ls command again, as follows:

ls /

Want to check out some of the directories you see in root? You could either cd into them and ls the contents, or just ls the comments directly as follows:

ls /etc

This would display the contents of the "etc" directory, which itself lives in the "root" directory. Notice that the command uses "/" + "etc" to create a path to the destination. In "etc" is another directory called "cron.d", and you can use the same principle to view its contents:

ls /etc/cron.d

You now know enough to look around the file system. Note that most GNU+Linux systems (like tilde.team) adhere somewhat to an organization scheme called the Filesystem Hierarchy Standard (Wikipedia link). This is another subject for you to read up on later.

How can I keep my things private, or share them with others?

As you explore the filesystem, you might bump into some directories that won't let you in. For example, if you try to cd into the home directory for the root user (not the same as the root directory), you'll see this error: "/root: Permission denied". This is because GNU+Linux systems maintain a "mode" for each file that limits which users can read, write or execute it.

If you don't own a file, then you can't change its mode. This is a basic security principle in GNU+Linux systems.

For the files you own (i.e. the files within your home directory), you can change the file modes yourself. You do this using the "change mode" command, chmod.

Each file has three permission levels: for the file owner, for members of the file's group*, and for all other system users. For each level, you can permit any combination of "read", "write", and "execute" permissions.

(/* Do a web search for GNU+Linux users and groups to learn more about this important concept.)

You can change a file's mode with chmod one of two ways. The first is a symbolic way in which you add or subtract 'r', 'w', and/or 'x' (read, write, execute) to 'u', 'g', or 'o' (user, group, or other). For example:

chmod g+x filename.txt

This gives 'execute' privileges to members of filename.txt's group.

You can also use chmod numerically, through which you may set the user, group and other permissions all at once. For example:

chmod 755 filename.txt

This gives the owner read, write and execute privileges, and gives only read and execute privileges to group and other.

Use man chmod to get a fuller understanding of chmod.

To get an interactive, visual feel for numeric file modes, try the tilde.team file mode widget

--

Finally, remember that 'testing.html' file we made above? Let's use that as an example of how you can control who can view your files. Use the following to make the 'testing.html' file visible in your website:

cd ## to return you to your home directory chmod 644 public_html testing.html

Now if you bring up the following URL (with your username) in a browser, you should see the testing.html file you made.

https://tilde.team/~username/testing.html

The End (of The Beginning)

There you have it -- you know about logging in, using basic shell commands, and the file system, and you're now self-sustaining (and a little more).

tilde.team is about community, but it is about community of individuals who work hard to learn. what you have just leaned will give you a platform on which you can learn by doing and trying things out.

Below are some other common programs you'll likely want to use. Most of these have man pages, so you can read more about them. Others you'll just have to try out to see how they work.

List of Common Programs

mutt, alpine - for email

wget, curl - for grabbing files from elsewhere

weechat, irssi - for irc

scp - for securely moving files between networked systems. this copies files (i.e. 'cp') over ssh, hence 'scp'

lynx - web browsing

cron - scheduling recurring jobs (job = sequence of commands, often stored in a script)

dict - dictionary for definitions and synonyms

aspell - a program for spell checking

motd - list the message of the day, which on tilde.team displays all the other commands below

some tilde.team specific programs

bbj - a bulletin board for asynchronous discussions

tilde - a manager for user-submitted scripts

webirc - register for thelounge webchat (in case you don't like weechat or irssi, or want to get push notifications for mentions and query messages :)

chat - open weechat preconnected to our irc

Some shell use cases

And in this corner, we shall describe some common activities people perform in a shell... [Feel free to add here.]

Other Intro-to-Linux Material

Not suprisingly, you'll find a lot of other intro material online or in your local library. Here are a few that have been mentioned by tilde.team members:

Terminus - an interactive game-like introduction to shell commands http://www.mprat.org/Terminus/


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